Do you have a good April Fool's Day gag?

Since none of us share Fluther with people we know, I thought this would be a great place to brainstorm April Fool’s Day ideas. We can compare notes later, too!

Here is an idea I stumbled on and love. I am going to do this to my neighbor. She’ll get it when she opens the door to go to work that morning. I’m planning half helium, half lung air. I can’t wait!

What ideas do you have? What have you done before? Who do you play your jokes on? Have any of them backfired on you?