Kill or be Killed
Used as an answer for someone asking you why you did betray them while you two (or more people) where a Team in a game where playing in teams wasn't an option but you decided to be team anyways, the answer makes reference that, even being a team, at the end of the game, it was still Everyone vs Everyone, and you only used them just to achieve your goals easier via manipulation, trickery, and similar
Example:
Guy A: *gets killed by his partner while playing Skywars* DUDE, WHY DID YA KILL ME?
Guy B: because it's KILL OR BE KILLED buddy, and you FELL IN MY TRAP
Guy A: *gets killed by his partner while playing Skywars* DUDE, WHY DID YA KILL ME?
Guy B: because it's KILL OR BE KILLED buddy, and you FELL IN MY TRAP