This cheat requires two controllers that must each be signed into seperate profiles.

Go to multiplayer and set the game mode to Sabotage, then set the game rules to one life per bomb and the bomb timer to five seconds. The rest does not matter.

Start the match, plant the bomb and quickly run to the second player.

As the bomb explodes headshot the second player and you get 10,000 exp every time.

[unconfirmed]