I've always been on the generous side of tipping unless the service is bad.
Most embarrassing tipping moment: I organised a work social with maybe 20 people at a restaurant and one of them used to be a server. He made us all wait 20 minutes while the "automatic" 10% tip for large groups was removed from our bill because as he said "it isn't automatic". The service hadn't been bad - I tried to interject after I eventually realised what was going on but as the new boy I was shouted down.
I once paid for a meal with a card and didn't know how to add a tip (too much wine I think). I popped back a few minutes later with a tip after I got cash out of a machine. Got a big smile. It was a great meal.
MMXIV