I'm one of those people who never had to work as a waitress or anything, but I still tip A LOT. I just feel bad for how shitty people treat waiters/waitresses. So I always tip the pizza guy, the carhops and the waitstaff way more than necessary.
I have seen some people completely chew out and go off on waiters for minor things and I don't know how they stand there and take it without bitch slapping the customer! Guess that's why I've never worked in that industry.
I don't usually let my husband do the tipping because he has certain rules (like his glass can never be empty) that decreases the tip by a percentage each time. It's like a little formula he uses. He tipped a guy a penny once (and the service WAS horrible) instead of not tipping at all, just to insult the guy. We still go to that restaraunt all the time and we've never gotten that guy again. This happened like 2 years ago or something. If we get seated in his section, he gets another person to cover for him. I still feel bad about it though, but I'm more forgiving than my husband.