Well, this will make your friend (and maybe you somewhat) happy:
The GameCube's main launch game, Luigi's Mansion, stars Luigi and only Luigi. This is the first solo game that he's in, and still no word of Mario appearing in it!
I don't know who else is with me on this, but not having Mario in it would not ruin the game. Heck, I'd buy Luigi Party or Luigi Tennis if there was one.
Try to get this through his head: Even if he hates Mario, have him try out the Mario games. I hate Pokemon, but I enjoy Smash Bros. (beating up Pikachu, no less).
Ok, so I lost my mind back there. So what?
Peaceful penguins, demented dragons and growling griffins, oh my.