I like practical jokes -- but only the surreal, positive, uplifting kind.
Our local DVD rental place disappeared a few years ago. But about a month ago we started using the self-serve machine in front of the local grocery store.
Last week I was returning a DVD (Project Almanac; I liked it), when -- on a whim -- I slipped in a $5 bill and a note saying "Congratulations! You're (apparently) a winner!!!"
And on Friday at work, whenever I rode the elevators I'd leave a coin on the floor -- just for the next person to find.
So: it amuses me -- but it makes people happy, rather than sad.