Life is easier if you just always tip 20% no matter what. I go to restaurants to eat. It’s not my job to judge the waiter, and who am I to judge someone I don’t know on a job I’ve never done?
Tipping is stupid, yes, but that’s the culture and people need it to live. Only exception I make is if a restaurant has a required gratuity (usually 18%), I don’t tip any additional.