They had a 'witchy' old lady next door that was constantly complaining about everything and everyone in the neighborhood. After one really good round about kids and pets messing up her spotless front yard, my buddies planned what turned out to be a better joke than they originally thought. Juvenile as we all were, they planned to write some dirty words in her meticulously-groomed front lawn with some kind of powder that would stand out. The only thing they could find was some Ortho Super-Gro Lawn Food (white powdery stuff). They wrote the message in the dead of night, and next morning it was bold and white for the world to see. The 'kicker' came after. She came out, saw the graffiti, and immediately grabbed a hose and WATERED IT OFF!
To this day, those sections of grass are just a little bit greener than everything around them, and the words can STILL be read!
This reminds me of a story that a former roommate related to me. In college he and a group of friends got revenge on complete strangers. ....Well, let me set up the situation.
Y'know how sometimes you gotta park real far away from your destination because certain types of people like to take up two parking spaces...? Well, he and his friends got a little ticked about this, especially during weekends at the school. One day, they decided to get even with every verb+"#@@#$#@$&&"+ that took up "their" space. They turned the car sideways. As he said, "He wanted that space so bad, now he can have it for a loooong time!"