Someday they're going to carve your head on Mount Rushmore

The episode where Oscar says to Felix, “Felix someday they're going to carve your head on Mount Rushmore... if I don't do it first.” For all these years that I’ve been watching the show & have seen this episode I never really understood the joke or what Oscar meant. Not ashamed to admit that I just didn’t get it, but if anyone else does then please clue me in.