It's very rare that I won't tip at least 10% unless the service is extremely bad. As long as whoever is serving me is somewhat competent, reasonably pleasant, and seems to give a shit, I tip 15 to 20%. Service jobs suck and the amount of abuse they receive from customers, management, etc is pretty staggering. That's not an excuse for them to act like douchebags, or give crappy service, mind, but it is something to think about. If people didn't tip, the vast majority of these people would be making income that nearly qualifies them for the poverty line. Alot of them do anyway. They depend on their tips for a basic standard of living. It doesn't bother me one bit if they don't report part of their income. And honestly, this image that some people have that waitresses, bartenders, servers, are not reporting tens of thousands of dollars in income, and they're pulling down 70, 80, 90 k a year is pretty silly. Maybe some of them do, but the majority don't. Also, it just makes good sense. Especially bartenders. You tip well, and you don't even need to tip pretentiously well, just 5 to 10% more than standard, and you get better service. They know your drink, you get bumped to the front of the bar sometimes. People who tip pennies or quarters to 'make a point' can shampoo my crotch. The only point they're making is that they're douchebags
Having said all that, I don't believe in tipping standard for bad service. I'll usually leave something, unless I'm really pissed, but if they haven't earned 15%, I'm certainly not giving it.