In the US: Big franchise / chain -> never ever tip. The employees are disposable and I'm not going to reward a system that makes billions while paying nothing to its employees. I'm not worried about them holding a grudge or whatever because they already can't remember me from one visit to the next, it's so impersonal and unfriendly anyway. The kids behind any counter never remember me. Even when I still gave a fuck and tipped and was cordial, they never remembered me. I guess we all look the same.

But also over the past few years I've been to fewer and fewer large franchises and they've gotten more and more aggressive.

Small restaurant -> I always tip. I grew up as an immigrant in an immigrant restaurant so I relate to these people. They also remember me, my family, and engage in small talk, ask how my parents are doing, etc.

Overseas: Restaurants/stores: never. (they almost never ask for a tip but it's starting to become common in the UK). But always carry cash on the streets because there's always somebody who needs it.