The Game -- Rapped About Banging Kim Kardashian ... I Also Hit It First

The Game didn't outright say he boinked Kim Kardashian back in the day ... but he did rap about it on a song with Ray J called, "I HIT IT FIRST"

TMZ obtained an early demo of Ray J's infamous song ... turns out Game was originally featured on the track -- and it sounds like he's rapping about hooking up with Kim.

Game is cryptic with his XXX lyrics -- but makes reference to her store "Dash" ... and says he'll show people how to really "drive that ghost" (seemingly talking about Kim's Rolls Royce Ghost.)

He also raps about getting oral sex from someone in a private jet.