The reason that tipping has begun to become an obligation in America is that the servers are only paid $2.13 an hour in most states. Not to mention that fact that they are taxed automatically assuming a 10 or 15 percent tip on all of their sales. (This varies from place to place, and is not true everywhere). But basically that waitress is paying taxes on that tip even if you don't give it to her.
If you don't tip it actually can cost them money to wait on you. How would you feel if (say for instance), you were a programmer, and someone called you up and said this.
"Hey, I need you to write this program for me, and I am going to complain about every aspect of it, but I am not going to pay you, and the IRS is going to tax you as if I did!".
Would you be happy with that?
If you live in a country where tipping is expected, and you are being waited on by someone who depends on your tip to feed their family, then you really should be tipping. Otherwise you are theoretically depriving someone from the lower class from a bit of their weekly income. If you were not there, then they would have waited on someone else, that someone else would have probably tipped.
You don't have to worry about any crazy formulas or algorythms to determine how much to tip. Just tip whatever you want to give. Just make sure it is something, even fifty cents will at least cover the income tax that the server might be paying on your supposed tip. If anything I tend to tip higher at the cheaper restaurants. The servers at those places usually make about half of what the people at the fancy places make. The servers at the very best establishments may possibly make quite a bit more than you. But the ones who work at the cheap diners tend to make only slightly more than a fast food employee.
If you are a server I suggest getting to know your regular customers, trying not to make mistakes, and apologizing when you do. Save that brilliant "personality" for people who actually seem interested in speaking with you. Plenty of people just want to get their food, without having to put up with your amateur acting.