I managed to play 3 pranks on myself today.
Taught my cat how to leave the house by the cat-flap, but not how to come in by it. (Or maybe he just doesn't want to.) Thus, I am constantly his doorman. This took some setup, the best pranks do.
Got a minor amount of hot pepper in my eye, then forgot about it, washed my face, and got the rest of the oil in my eye, leading to a farcical dance around the kitchen.
Unplugged my dialup gateway to save power overnight (sun has been scarce lately), and had a "how can I be online" moment hours later. Forgot that I've been using a power-hungry laptop there as my nslu2 is ill.