I've had many hilarious ones, but here are some:
My friend's t-shirt was short, and while he was sleeping, i drew in blo-pen, a sentence that said above his butt: Insert here, men only. He also bent over when we threw his pens on the ground, and almost every teacher saw it.
Another time, in Spanish class, the teacher woke a sleeping student, and he flipped over the desk and started cursing and screaming because he got scared. He's 17, left back twice, and dropped out of school 2 years ago.