Here's one from when I was a kid (wife say's I'm still one). With the fourth right around the corner,I know you can get these, The snap and pop things that you throw on the ground and pop-well take about 5/6 of them and put them under a toilet seat. As long as the next person sits on it they will pop rather loudly when someone is least expecting it. Just alittle fun -nothing blowing up or anything. Just put them under the little leg things and set the seat down gently.