Thanks to Mauro, I am a lot into grape racing lately: here is how it works (taken from here:
What you need is a microwave oven, some grapes, a small measure of sunflower oil and some friends with which to compete.
The idea is thus. Firstly, if the microwave is of the type that has one of those silly rotating dish-like things, which rotates your food to make sure it gets cooked evenly, then take it out and throw it away. You won't need it for this game and, if you get addicted enough, you probably won't use your microwave for anything else, so you won't need that dish thing ever again. OK, next, lightly cover the floor of the oven with a small amount of sunflower oil. Just generally spread it about, to make a thin, lubricating layer, on which a grape may skate about. Try it with a practice grape to make sure you've got it right. Then, line up a number of grapes at one side of the oven, with one grape corresponding to each player. Important tip here--make sure that the end with the hole in it is pointing at the wall. This is really quite fundementally important. Next, lay bets--or whatever--on your grape, that it will win/lose/finish in a particular position or state/ whatever. Then, set the microwave to full power, and switch on. What happens is that the inside of the grape heats up, liquifies, and acts as a jet propellant to push the grape along the lubricated floor of the microwave as it shoots out the hole at the back. Thus, each grape travels with varying degrees of speed and/or success across the floor. The first to reach the other side of the oven is judged to be the winner, or, failing this, the one to travel the furthest. Some grapes don't make it even this far, and either shrivel up or explode messily on the starting line, but this just adds to the fun. Remember to switch off the microwave and remove the competitors before replacing them for the next round.
The game can be varied according to players and their individual tastes, like ``Strip Grape Races'' for example, or ``Stunt Grapes'' where the grape must perform a task like jumping over other grapes, etc. These, and other variations, should keep you and your friends amused for hours.
A video can be found here: