However, unless you know that the janitor is a real asshole, I wouldn't make him or her the victim. They have enough shtit to deal with without poop juice shooting up at them. Hey, Sexy Take someone's e-mail address who you know to be something a prude and sign them up for free porno pictures. This is another great one beginners. However, some subscriptions require a response in order to become active.
Porn sites play pretty loose with the rules, though, so good luck.
In fact, I have a feeling somebody did this to me. In your car, turn the windshield washer jets sideways so that they shoot sideways and out from the car. Then, go to a crowded area with sidewalks, maybe a shopping center or something, and drive by people and fire away. They'll never know what hit them. The washer jets are not adjustable on newer cars, so this might be difficult to pull off, at least logistically.