My teacher is a he.
During class, tap your pencil on the table, slowly tap harder and louder until the teacher looks, pretend to write. Keep doing it louder and louder. If the teacher asks who is doing it, and a kid reports you, deny it.
Take a friends pencil and write "Touch me if you're gay" on the side of the pencil and leave it.
Re-arange things in your friends backpack when they're not looking.
When in computer class, play the Windows XP Critical_stop sound on full volume over and over
write "cigarette sits here" under the desks