Just get out, leave a note or a letter with all the things you found annoying, just let all your feelings out, no prank can hurt more than a sincere letter.
Don't do all this prank business, its childish and not worth it. You ain't gonna be there to laugh at it either, and when its a mild prank on friends its taken in good spirit and everyone laughs at it and remember it later in life, this however is something that you might have fun setting up, what happens next? nothing, you have no clue, and I doubt you'll laugh about this in 10 years saying "yeah i showed him by puttin mayo in his shower".
I have had terrible experiences with room mates as well, and I was waiting to get out, and thats all I did. Move on, concentrate on more important things, feel good about yourself that you have been so tolerant to such things cos it helps as you face tougher scenarios ahead.