I read in Linda's blog about the tradition of toilet-papering a house in the States. That's relatively harmless, but of course as she points out, on a rainy day it can turn into a sodden mess.
I can tell that in continental Europe, anyone getting married is fair game too. Filling the nuptual bedroom with balloons is a nice one. Another one does cause quite a mess.
It involves placing a can of shaving foam in the freezer at -18C / 0 F overnight. For the ladies, shaving foam comes as a liquid under high pressure in a canister. The next morning, the happy couple toddle off to church. Meanwhile, the evil culprit peels the can off the cylinder of frozen foam and places said cylinder in the middle of the bedroom. By the time the wedding and the reception are over, it'll be well after midnight. The shaving foam will have filled the bedroom wall-to-wall with foam after it expands upon thawing.
I do not accept responsibility for the consequences of people following this information. Not all types of shaving foam are suitable, and serious injury and damage can result from puncturing an aerosol can.