I used to waitress and I have to say that I rarely, if ever, had someone leave less than 15%. The $5 tip was insulting and the waiter probably just blew up because I imagine it was one of the worst tips he had ever received and the table was full of drunk people who just shared a bottle and some appetizers for two hours. And btw. why didn't anyone break a $20? Come on.
I'm really surprised by the attitude here though - waitressing is hard, being on your feet, dealing with rude people, including drunks, and you don't make as much money as people think because of slow nights and the whole $2 an hour or so that you earn. I don't think waiters and waitresses have to "earn" their lousey 15% tip - seriously do you not tip cab drivers, or your hair dresser, or a bell boy for hailing a cab. I tip over 15% for great service and 15% for adequate. Plus in high end restaurants, yeah we usually do leave 20% on a bill that is a couple of hundred - because you have several people waiting on you and unless I'm ordering a very expensive bottle of wine, I think its normal to leave that much. There is really very little empathy here for people that work a hard job - all of this about it being there "choice" makes me rather ill, some of these people are working through school or didn't have quite the opportunities that others did, some like waitressing.
I'm an attorney now and frankly its a deal breaker for me if I go out on a date with a guy and he's a cheap tipper or treats the wait staff rudely. I also haven't forgotten how hard I used to have to work for that money when I waitressed. Sorry but I think it sort of rocks that the waiter told you guys off because it seems like you would have just done it again otherwise.