I usually tip 20%. I sometimes get confused for room service and some places in Europe where gratuity is included. When I tip when I shoudn't I sometimes feel like Vinnie.
Everyone should tip like Vinnie.
[Vinnie palms off a $100 bill to Barney]
Barney Coopersmith: You don't tip FBI men!
Vincent 'Vinnie' Antonelli: Sure you do!