I've spent about 10 years involved in the restaurant industry, from line cook to server to bar manager.
I get my hackles up over this subject.

This stuff may sound harsh but it's business:

In MA, restaurant minimum wage is around $3 per hour. It's typical that restaurant minimum SUCKS and is NOT a liveable wage. No tip=no food on the table at home.

A really SHITTY waiter should be reported to the manager, ask to have a new server. It's doing the bad one a favor. Trust me on this. I've told a waitress, VERY early in the meal, that it's in her best interest to just hand me over to someone else simply because I wasn't going to be worth her time in the end. Often it's a new waitress who just doesn't GET it yet, and needs more training. If not, she should probably find another line of work.

An average waiter gets 15%.
A cheerful and helpful waiter gets 20%.
At a diner, where the food is cheap, it's not by % of the check, it's by how much of a pain in the butt my order was. Like, a buck for a coffee, 4 for a full breakfast. Diner waitresses bust butt and get the shaft on the regular.
Bar staff starts at a buck a beer or mixed drink, less per-drink if you're ordering multiples of the same thing or a round of just beers.
Sushi/tappan/Mongolian grill chefs should also be side-tipped, but there's no set rule for this- they are paid better than waitstaff and tipping is courtesy rather than an expectation.

And don't give me that bullshit excuse ooooh the food is too expensive, I can't afford to tip. THAT'S WHAT MCDONALDS IS FOR! If you can't afford to tip, go to a counter-service restaurant where you have to bus your own tables.

Okay there's my morning rant. Hope you found it edumacational.