Other forms: frenemies
A person who pretends to be your friend in order to steal your ideas, compete with you, or gain some sort of advantage over you is not really your friend at all — they're your frenemy.
The word frenemy blends friend and enemy to describe someone who acts like your buddy but is actually a sneaky rival. It’s that confusing friendship where you’re not quite sure if they’re cheering you on or secretly trying to outshine you. For example, think of two classmates who seem friendly but are always trying to one-up each other in school — that's a classic frenemy situation!