In the US its defacto obligatory, which is fucking bullshit. The only reason I tip in restaurants (the rare times I go) is because I don't want a server to do something disgusting to my food if I were to ever come back, but I tip the bare minimum. IMO restaurant owners are scumbags for underpaying their employees and making them rely on tips. I try to avoid getting in situations where I need to tip, and often decline service staff trying to "help me" and I never have food delivered to me. Some fast food places now have a tip option for simply handing your fucking food over, but I never give anything. And when I tip, I always tip with my card --- that way they're forced to report it to the IRS as income, as the digital trail stays recorded; cash tips are basically under the table and are often not reported
I'm a prick, I know