Almost best car prank...

Twenty-something years ago, as a high school auto shop student, one of the kids in my shop class admitted he only took tech to get out of regular school, was a rich snob kid, and drove the 3 year old BMW that his daddy gave him. He had it in the shop one day to clean and detail it, and "somebody" slipped 2 pie pans, one inverted on top of the other with the edges taped and containing a decent size ball bearing, under the passenger seat. Every time he accelerated, "DOINK". Every time he braked, "DOINK". Every time he cornered hard, "DOINK".

In the following two weeks, that car was in shop class 4 times, was taken to 3 garages, and one BMW dealer. He was pretty pissed when some one found the cause! Oh, and because of his verbal description of the noise, everybody in shop class called him DOINK the rest of the year.