Go into multiplayer mode. You'll need at least two controllers and two human characters in the same team. Go to the temple and have the first guy go upstairs where you go to get the rocket launcher. That same player must stand over (somewhat float over) the hole where you come out of going up. Then, have the second player go under the first player and press "Z" to stand up while under the first player. The first player should die.
Similarly, if a player crouches and then stands up while being jumped on, the jumping player will die. This requires good timing.
Submitted by: PATATE11