a buddy
A buddy is a fake friend who thinks they’re cool until they realize you’re better than them. They stick around for about two months until something big happens, like you out-slang them in front of everyone.
Yo, I was your buddy last week, now you’re the king of the block!
I thought we were buds, but now I see you’re the real deal.
Buddy? More like buddy-who-just-cried-in-the-bathroom.