My grandma used to tip $.50. No matter what. Cup of coffee? $.50. 7 course meal where the bill was several hundred dollars? $.50.
Both my parents tip 15% max, pre-tax. And in Seinfeld-ian fashion, they round down.
I'm a 18-19% post-tax tipper at restaurants. Shoeshine? I'll give the guy or gal a 20. Bars? 2 bucks a drink. Crew transportation? 2 bucks a ride.
Also, for the love of all that's Holy, please stop talking in the van about how much money you make. I'm sure the van drivers would appreciate it.