I was out eating dinner with friends yesterday for my birthday and we had a pretty good time even though the food was pretty lousy. Comparing it to my solo dinner at Del Frisco's the other night, I began to see how two phenomena from my social cognition days (psychology was one of my three majors back in college) manifested themselves when people go out to eat.
The first is cognitive dissonance. Basically this theory is that our minds prefer our thoughts and cognitions to be consistent with one another. So when we go out to eat with a bunch of people, and we're all dressed up and paying 18% enforced gratuity for our group, we really don't want the dinner to suck. So we find ourselves more eager to say the food was satisfactory than if we were just stopping in someplace alone.
The second is groupthink. This is where people's reactions in a group dynamic tend more towards reaching consensus and avoiding conflict and critical analysis. So if all your friends seem to be enjoying their food, you'll be more likely to shut up about the fact that your food seemed mediocre and start thinking that perhaps you'll like it more with a few more bites.
I'd like to reference some studies here but don't know where to start so I'll just say that I got my information from wikipedia and that there are references there for anyone who wants to know more about those topics.