Here are my few contributions...
On April fools one year, I removed every single light bulb from my (then) boyfriend's house, jumbled them up, and hid them throughout his home. He came home in the afternoon, and it took three hours for the sun to set, and for him to figure out what I had done, and another two hours to search down the bulbs in the dark. I helped him though
When my husband and I married, his family broke into the house on our wedding night and put 20 pounds of rice in every nook and cranny of the place. It was in our socks, the pockets of all of our clothes, in the cupboards, in the cups, between the plates, in the drawers etc. etc. etc. When we left for our honeymoon, my husband unzipped a pocket on his luggage to stash his boarding pass and rice poured out all over the airport floor. It's been nearly five years, and I'm still finding rice.
Finally, I recently went to my friend's cubicle and stuck googley eyes to all of her office supplies and plants. It had a nice effect.
Another one I like is putting "invisible" tape on the handle of the little kitchen sink sprayer, to hold it down. The next person who turns on the sink gets a nice shower.
