I dunno which is g@yer... you making a thread about this or actually sitting there while the bed is rocking and listening to him.
You must be the world's biggest ***** if you can't A. say "I know you're not jerking it up there." or B. LEAVE.
I don't care how tired I was if my roommate went to the bathroom to get tissue first off... then climbed up on top of me and started jerking it so hard the bed was rocking I would definitely express that I don't want that to ever happen again.
You guys must have a pretty close relationship if he even tried. But seriously, grow some balls and say "I can't believe you are going to sit there and jerk it while I'm right here." Then if he doesn't stop just leave and tell him you are going to punch him in the face if it ever happens again...