This is my favorite joke from junior high. It is a two person joke, so you may need to try it out on an innocent bystander.
Me: Ask me if I'm a tree.
Innocent bystander (looking dubious): Are you a tree?
Me: No! (hysterical laughter)
I don't understand why I still find this so hilarious, or why I'm laughing as I type it out. Most innocent bystanders do not find it amusing. It's a lot more fun to be Me ;)