Do you say something when someone is not wearing a mask?

I think that this is tricky--people generally don't like to be told what to do, and so saying something about mask wearing seems likely to make people defensive, rather than change their behavior. If I am out in general public and someone is not wearing a mask, I don't say anything--but just move away. I do think that the situation you described--a business--is different.   In this case, maybe it's more effective to leave and then call or email the business and politely say that you came in and left because employees were not wearing masks.  I would assume that if a business wants customers to come back, they would address this with employees. And if it's a manager that isn't wearing masks, then good for that person to know that it matters to customers. You could also say something as you leave the business, but if you are talking to employees and not the manager, that may not have much impact. 

It depends. If it is a store or restaurant or another place where I am a customer and it is employee not wearing the mask then I would leave and say something to the people there that I'm leaving because I don't feel safe there due to no mask by employees (if the employee in question is interacting with customers or food and so putting me at risk) since it makes it my business and I feel ok saying something.  If it is just another customers I will stay away from that person or maybe step out and go back in when they leave, I generally don't feel it is my business to tell another customer what to do and will just stay away from them.  With employees it is different since I have a right to let them know that I won't purchase from them because I don't like their safety/hygiene standards and then will leave. 

I tell any frontline worker “thank you for your service” and if I see they are not wearing a mask, I remind them to. I am so grateful for the work they are doing and I wouldn’t want them to lose any business because of something so small. 

As for mask wearing...

Why? My spouse is working with patients who have COVId everyday and we are always potential carriers. We’ve lost two friends to it. 

Do masks work? We don’t know. The N95 masks do. The others may or may not. At this point, they are a sign of respect - that this is being taken seriously. If someone is preparing my food and they sneeze and don’t cover their mouth or nose, would you eat the food? 

I encounter this situation with friends in passing (we continue to distance because we are potential carriers). With friends and family, I have to say, “ah you don’t want go near us!” And “oh my mask is falling” to remind them. If they don’t catch the drift, then I say, “if you don’t wear your mask, that’s fine but I have to stay apart from you.”

***For the record, three months ago, I was making fun of wearing masks and I really, really despise them. 

I don’t say anything. Not my business.  But if was a restaurant worker, I wouldn’t go there again. 

The mask issue is tough.  Realize most counties in CA have NOT mandated masks and the numbers in these counties seem relatively stable.  Social distancing seems the best way to avoid the spread of covid.  CDC guidelines also do NOT mandate mask wearing and are just a "recommendation" and only in close quarters where social distancing is difficult to do.  

I personally would not say anything and I still would frequent that business.

If the person is serving you in a store, you don’t need something clever to say. I was in the Monteray Fish Market, ordered prepared salad. The gentleman behind the counter had no mask, no gloves and had his finger in the container. While you can’t catch COVID19 by consuming it, the whole thing was unappetizing. I just told him he needed a mask, gloves and to keep his fingers out of the food. He was perfectly polite, and apologetic. He dumped out the contents, put on a mask and gloves, gave me a new serving and told me he was tired and just forgot. End of issue.

With people you don’t know but see around you, that is more complicated. I see more and more people not wearing masks. A few days ago, at Semifreddi, I saw a family waiting on line, they all had masks, except for a very elderly woman who was with them, who was obviously experiencing some sort of dementia, and kept wandering off, and was approaching people randomly to say “ hi.” This was obviously a problem for a number of reasons. I attempted to ask them why she was not wearing a mask, and they ignored me. Suggestions welcome!

Was the person wearing glasses? Wearing a mask tends to make your glasses steam up and then you cant see. If nor, it is very difficult to eork a 9 hour shift, especially somewhere hot, like in a kitchen preparing food, while wearing a mask all day. Its hard to breathe.
I dont think you say anything, i think you did the right thing by deciding whether or not you want to stay, and then leaving once you decided. You make your choice. But if you're not comfortable you may have to start preparing your own food and buying a months worth of non perishable foods so you dont have to go to the store.

Risk of virus spread is really complex. From my understanding (always read the sources yourself), you're trying to avoid a critical mass of viruses in your system.
So, it's exposure * time.
Breathing doesn't shed a lot of virus, so you would have to be in an enclosed space with that person for a long time, on the order of an hour. Breathing through the nose sheds less than the mouth. Talking sheds more, and coughing is something like 4 orders of magnitude more viruses, with sneezing being two orders more than that.
So if someone sneezes, get out of there.
If they're asymptomatic and in contact with your food for two minutes, it seems low risk. They're more at risk from belong in an enclosed space all day with lots of outsiders entering
In the end, your comfort level should determine whether you stay or go. If you're going to panic about it later, it doesn't seem worth it.

Absolutely not.

Cloth face coverings (let's make sure we understand the distinction between those and "masks") currently function as a visible sign of public-spiritedness, conscientiousness, and compliance; and of course current regulations require those of us who can safely do so to wear them in certain public situations.

They might in fact help to a very small degree to slow the spread of disease, but though it's socially unacceptable to say so, the evidence is minimal. 

From the Chronicle: "Homemade face coverings may prevent the spread of infected droplets by asymptomatic individuals, but they provide significantly less effective protection than surgical or N95 masks. The CDC primarily recommends using these to keep the wearer’s face clean and reduce the likelihood that people will touch their faces."

Of course we should wear face coverings ourselves, but it's beyond intrusive to run around acting like amateur enforcers. Remember that stress in itself lowers resistance to disease. 

We were waiting for takeout at a restaurant.  There was a sign on the door saying all people must wear masks.  A man breezed in with his young son without a mask to pick up his food.  My partner said "you're supposed to wear a mask" and the man screamed "F*** you!!!" in front of all the others waiting (with masks) and his unmasked son.  Wonderful.

In response to the person who said that cloth masks don't help:

Reuters (6/9) reports that research suggests “population-wide facemask use could push COVID-19 transmission down to controllable levels for national epidemics and could prevent further waves of the pandemic disease when combined with lockdowns.” The study “suggests lockdowns alone will not stop the resurgence of the new SARS-CoV-2 coronavirus, but that even homemade masks can dramatically reduce transmission rates if enough people wear them in public.” The findings were published in the Proceedings of the Royal Society A.

I wouldn't bother.  Pre-covid, workers have been exhaling on our food forever and I haven't read anything that suggests that one can get infected by ingesting food with the virus on it.  The face coverings that I've seen in businesses are so loose that even if the nose were covered, everything would come out the sides/top/bottom immediately anyways.  Uncovered, nostrils point downwards so the net effect is probably similar.  If you've ever seen smokestacks, aerosolized particles expand to fill a given space, so whether it shoots down from the nose or around the sides of the mask, I simply assume that I am out of luck if I am within the worker's personal space bubble.  Maybe the worker is inhaling through the nose and exhaling through the mouth?  Anyways, I won't go so far as to say that the health orders are ineffective, but I will say that in the ideal world where people didn't have to buy/produce their own face coverings, the health order would call for properly fitted N95 masks with exhalation valves.  Everyone would be able to protect themselves this way, as comfortably as possible, without relying on someone else to be courteous.  I did a random test measuring my blood oxygen level while sitting in a car doing nothing but engaging with my cellphone while wearing an unvented N95 mask.  After an hour my blood oxygen level fell about 1%.  I'd recommend that you all try the same experiment but while preparing food or cleaning the house, or reorganizing the garage over the course of an hour to see how uncomfortable you get.  It's not fair to judge people on the basis of something horrible that might happen when they are living an unpleasant experience that is definitely happening for lengthy working hours every single work day.  Don't assume that they're ignorant or arrogant.

I'm in a very high risk group and I feel very upset when I see people not wearing masks appropriately. Especially if they are indoors and/or preparing food for sale.  My doctor has point blank told me to avoid all take out for this very reason--she feels that she routinely seems people doing food prep not wearing the appropriate PPE.  When I have encountered people either outside or in other spaces I have straight up said things to people when they were coming too close to me and not wearing masks or asked people about to pass me if they have a mask and could they put it on.  Many are obliging. But some do not even have masks with them and then I have said, "You are supposed to have a mask in case you have to come close to people."  I've received a wide range of reactions--from friendly and understanding (when they see my 8 month pregnant bell) to people telling me  F off.  I just try to mostly focus on modifying my own behavior to minimize risk but the truth is the mask I wear all the time protects others...so others' masks would actually do much more to protect me.  I wish more people would understand this.  In terms of a business, I would ask for the manager and point it out or call back at a later time and ask for the manager and say that you saw it.  It is not right for businesses to fail to comply and most business owners would be upset I think if they knew folks were not complying and it was (understandably) impacting business. It's definitely hard right now when some people seem to be wanting to return to business as usual and others are still very much following the rules--and the disease rates keep increasing.