Caniprokis is more correct about tipping than Calliander.
Tipping is a social etiquette. There is no 'standard rule'. An etiquette belongs to the society. There are lots of totally different societies. You are part of just one.
Tipping in the society Calliander and Caniprokis belong to generally means 15% for lunch, 20-25% for dinner. Other societies, such as Europe.. leave no tip unless for exceptional service or large groups or something 'extra'. Actually, it's that way in MOST of the world.
Generally means just that.. generally. Dinner for instance is more work (you have salad and extra things for a larger meal). Groups over the size of four are going to be more work too. Once you have five, you have a non-standard table. There is going to be less area for plates, etc.. hence more clearing, more drinks to carry, etc.
Personally, a waitress at a restaurant should get nothing if they are HORRIBLE. But, if they are that horrible, you should also complain to the manager. So, leave a tip unless you want to tell the manager about the bitch. For lunch, leaving 6-10% is fine for bad bad service.. but your lunch is going to be cheap, so 15% is reasonable.
For dinner, you shouldn't leave less than 12-15% for bad service if you are going to go back there.
If you are dining with others who tip more than you.. GET A SEPERATE CHECK or TIP THE SAME PERCENTAGE. When you decide on a percentage at the end of the evening.. ITS A TABLE PERCENTAGE. Not "Well, I didn't get a drink.. why should I pay for refills?". Too bad, dick. Get a fucking seperate check.
Arguing about the bill is bad too.. UNLESS two people want to pay it and they are fighting over who gets to pay.
If someone buys you dinner, return the favour on some level.
For delivery, I like the buck and change system for small orders, especially when sober. So, if your order is $11.45, you give the guy $13.00. If you are stoned, let the fat kid lay down his fifty-dollar-bill and act so stoned that you don't know what change is.
I only recently learned about hte tipping for hair cuts. I don't quite get that one yet.
The toughest tipping is the driver situation. Like, the hotel van picks you up at the airport. I tipped using $2.00 bills :). It was classy. One dude only got two bucks because I carried it all. Another got $8.00 cuz he carried it and it was sorta heavy. A big trip would be like ten bucks a person.
In Europe, if you still must tip for everything, tip only 50% what you do in the US...