I wouldn’t want my kids to hang out as an equal with kids who think that is a fine way to talk. Clearly it’s the “logic” of his peers that it’s cool. Your son is probably trying to measure up to this little cliques lousy idea of etiquette.

I tell my kids that they can be around anyone in the right measure, but don’t take on their ways. Like a track team it’s inevitable that some of your team members are going to act like jerks often, so you aren’t necessarily going to isolate , but you don’t have to jump into the stupidity with both feet either. Stand your ground.

Sounds like your son is experimenting, so he is kind in one set of circumstances, good, and rude or extremely rude in another, tell him to be better than that.