Go to level 1 (Bob-omb Battlefield) and enter the battle with King Bob-omb (first star). Climb up to him. After starting a fight with him, slowly lead him down the path of the mountain and he will eventually jump back up. Go talk to him again and he will accuse you of throwing him out of the ring. This is what he says when you throw him off of the mountain - but you didn't throw him off!
Submitted by: Mitchell VanRassel