A lot of people don't seem to notice that the ball of toilet paper was near THE ROOMMATE'S laptop and THE ROOMMATE'S mouse. The only thing the roommate is guilty of is using the poster's toilet paper and not putting it back. Also, it's unhygienic that he doesn't throw that crap away or flush it.
There is no precedent for revenge. There is no justification for revenge. Don't get revenge on your roommate. FYL.