A clock made in Bavaria (Germany), which ruins the meaning of the word clockwise.
The hands on a Bavarian clock all go anticlockwise. 1 is to the left of 12, instead of to the right. The clock is internally consistent in it's timekeeping; but it looks very odd to people who are so used to regular clocks because it is not consistent with external expectations of how it should appear. A mirror image of a Bavarian clock will show a clock that most people would recognise (except of course the numbers on the circumference will be reversed). A useful reminder that lots of things we see are arbitrary social values with no particular significance or relavence.
Also, an amusing trick to play on your stoned friends at 2am.