Hide the Xbox when he isn't home and tell him the tooth fairy took it.
then it overheated and froze.
Just buy a new 360 and give him the old one. Maybe explain to your mom that now that you both have one that it is completely fair and that if he breaks the one you gave him then it's his problem, not yours.
I'm sure thats financially unacceptable.
Can't you put a password thing on it?PS3 FTW :3