Any good suggestions for a good april fool's prank?

One of my good friends at work told us of a good prank her husband got on her one April Fool....he enlisted his supervisor at work to pull it off, though, since at the time he and his wife (my friend) worked at the same place.

He told her that he'd gotten fired, knowing she'd call his supervisor (who, remember, was in on the joke) and he backed up the husband's story. Needless to say, the next morning, all was found out, but even to this day, she STILL laughs about how he got her on that.

Okay, cows can walk up stairs, but not down them. Bring a cow up the stairs at your school, and leave it there. Or hide a crappy cell phone w/o caller ID in a classroom, set it to an annoying ringtone, and call it all day.