But the lesson is "it's not cool to call your friends fat" and "you can call out your friends if they're being mean" or even "avoid people who make you feel bad". You clearly got the wrong message here.

There are shitty people and we have to deal with that, but that doesn't make these people any less shitty. We know how social consequences work, and you think you know as well, but why you gotta constantly take the shitty people's side here? Unless... Hmmm... 🤔