I haven't observed this happening among my friends. Maybe if you only go out to dinner with homo economicus...
This is called the unscrupulous diner's dilemma, and experiments say that not only do people (strangers) respond to it like homo economicus, their utility functions seem to not even have terms for each other's welfare. Maybe you eat with people who are impression-optimizing (and mathy, so that they know the other person knows indulging is mean), and/or genuinely care about each other.
r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.