Tipping is big here in the states because our waitstaff get paid jackshit. $2.13/hr is the average minimum wage for tipped workers meanwhile the average minimum wage for non-tipped workers is $7.25/hr. Customers are expected to make up the difference. It's a shitty system designed to put more money in restaurant owners' pockets.Yes, I'm from Europe. Maybe it's a cultural difference with the US.
Anyway, I tip 20% on average service, 25-30% on great service, and 15% on crappy service (unless there was a reason for crummy service like the restaurant being super busy and/or understaffed, or if my server is just starting out).