This is a *great* FREE April's Fool trick to pull on people. It is harmless, and really does not do any permanent damage. You do drill a small hole into the faucet aerator, but the aerator will still function 100% normal when the blockage you create is removed. The result of this prank is a wet spot in your targets pants or shirt, making it appear that they wet themselves. While this may seem like a immature prank, I'm 59. That either says that the prank is FANTASTIC or that I am immature. I choose to believe the former.
Take a pencil or marker and put a mark on the aerator facing the front of the sink (put mark on the direction you want the water to squirt) Remove aerator by unscrewing it. (second picture) If it is tight, use a pliers to remove it. ( If you don't want to scratch the finish of the aerator, put a strip of masking tape of duct taps on it before unscrewing)
After you remove the aerator, push the internal screen and parts out of the outer metal "ring" Next, drill a small hole (1/16" - 1/8") through the outer metal ring at your mark. Next, you need to use one of the next two steps to create a blockage DOWNSTREAM of the hole you just made. If the aerator is a longer type, use this step. If this won't work because the aerator is too short, skip to the next step.
If you have a aerator too short to place the blockage below the hole, instead use a piece of tape over the final screen. Secure it by putting the internal part back into the outer ring, thus pinching the tape in.
Reassemble the aerator and screw it into the faucet. Make sure the hole is facing the direction you want the water spray to go. BE CAREFUL IF YOU TEST IT! or you will be the one with spot on their pants! The stream is quite forceful even with the faucet only cracked. Next, retire to your lair and watch for the fruit of your devious labors to appear.