The mere mention of "toilet pranks" reminded me of my older brother, a former plumber. He told me once that he felt he was treated unfairly by management of a store where he had made a purchase. He said that he returned a couple days later and asked to use the bathroom, whereupon he pulled out the large wooden cap from an old bottle of English Leather and flushed it. Sort of. It managed to get wedged it nice and solid deep into the toilet -- far enough that you couldn't get it out. Since the store was small, it was the only pot they had. He left, and no doubt they discovered sometime later that it was inexplicably blocked, with no relief from a plunger. I guess he had some small measure of revenge when they had to call a plumber in to remove or replace the toilet.
I remember asking him how he would have known to do that. He said he had been called for repairs more than a few times for just this very reason, and after a couple of times, had taken a sledgehammer to an old toilet he had removed, to bust it up and see for himself what the problem was. Apparently those caps were the perfect shape and size for causing problems.
Guess it could happen by accident, too. Later, he said he would go into a house where there were some little kids, and where the family was reporting the same blockage problem. He'd go into the bathroom, see the bottle of Dad's aftershave with the cap missing, and start shaking his head....