Take a dump in a pizza box and leave it in his room (when he won't be back for a while) with a lamp (preferably one that gets hot) on it. Pretty gross.

Leave a note that says more is to follow if he doesn't turn his music down.

If he locks his door, fill a pillow case with whipped cream or some other foamy substance and slip the open end under his door and then stomp the pillow case.

If doors open inwards, take one of the trashcans (55 gallon variety) and fill the thing up in the shower or something and leave it leaning on his door at night so he gets a little soak when he opens the door.

I've got more if you need em, but this is probably a good start.