A-1 Practical Joke

This can actually be either a straight practical joke, or an act of pure spite, depending on how you want to play it: All you need is a bicycle lock. It can be a cheap one, but of course the joke will go better if you shell out.

All you need to do then is find your victim's bicycle. Then lock it up. Hide the key, or throw it down the sewer. Congratulations. You have just played a practical joke. If you use a good quality U-lock, it will be impossible to get off without calling the fire department (or so I am informed on good authority).

I guess this would also work on motorcycles or hot dog carts, in principle. Try securing the lock around a car's axle. Really, the more valuable the item you can lock up the more fun you are going to have.

This is definitely the most efficient practical joke available to the public.