in my english class, we had this one student ask the teacher to make and enlargement of this thing on the photocopier. While she was gone, everyone in the class had turned their watches 30 mins ahead and we turned the clock on the wall 30 mins ahead and we even went as far as turning the clock on her computer 30 mins ahead as well.
when it was time to go (or so the clock said) we all left, walked around the school, and then came back (cuz she could've gotten fired for letting us out that early) and we all said in unison "April Fools".
lol
it was so good!!