As far as I'm concerned if the manager doesn't want to pay them minimum wage and they aren't capable of carrying out a decent service then that's not my problem, that's the problem of the idiot who decided to work at a place where they're not going to get tipped because everyone around them sucks.

Also, I suffer stressful situations on a regular basis but I don't get stressed. Do I earn anything extra for that? No. I don't. So if the waiter is stressed then again, that's his problem. I'm not going to pay him for it. Get a new job!