Replying to Funny School Days

To help make school go by quicker, my friends and I have started to make funny days. Today we made flyers that tomorrow was school wide bring your pet to school day... we handed out the flyers, and told basically everyone we saw to bring their pet to school tomorrow.... well of course our d-bag principal comes over the afternoon anouncements and says anyone bringing a pet into school would be in trouble, and why pets werent allowed in school and whatever blah blah blah.... just to be dicks i think were going to make a new one every week. make friday our school wide something day... any ideas for stuff that would be hilarious and cause mayhem in school? thanks