Leave. I hate crowds and the service will probably suck. Not how I want to spend my money. If I really want to try the place, I'll come back during off-hours.
Gosh this is a hard question. Too many variables. How long is the wait. How good is the food. Do i have to stand or can i sit while i wait. Can i have a drink while i wait. Is there a tv or do i have to stare at the walls. Do i have to wait in line that extends outside, and if so, is it raining or clear. How late is it. How hungry am i. How many people am i with. What do they want to do. Whos paying. Do i have to be somewhere at a certain time. Blah blah yap yap nag complain so on so forth.....
If you live in a large city, you wait for everything, even taking an elevator. In busy restaurants, it's common to wait 30 minutes or more. When I have gone to San Antonio by the Riverwalk, you wait up to 2 hours. Terrible!