There are some experiences you just never expect to have in your life. Like walking down the street and having a stranger rush out of their house and give you an expensive bottle of shochu for no reason at all, other than that you’re a gaijin. Or eating at a maid cafe where one of the menu items is to have the pretty maid slap you hard on the face. Or having someone come up behind you and push their fingers up your butt — that’s an experience I never wanted to have. This is a famous Japanese prank called kancho in which Japanese kids will sneak up behind someone and push their fingers into the buttocks area as hard as they can, essentially the local version of giving someone a “wedgie.” Back when I used to teach small kids I had to be on my toes if I wanted to avoid having some third grader sneak up and zap me from behind. Japanese students use mechanical pencils a lot, and another common prank is releasing the pencil lead a millimeter or so then pressing it down against the desk, so that a small piece of pencil lead flies with great speed at the person you want to torment.
If you teach ESL to kids in Japan, grow eyes in the back of your head.