There is a light tap on my classroom door. I'm not quite sure if someone knocked or not but I go to check anyway. There is no one there.
About 4 months ago, during the regular school year, several senior students were caught playing nicky nicky nine doors in the science wing. At first, I thought this was a repeat of that prank. One of my students saw the guy through the window and told me he had walked to the left. I went out into the hallway to confront him.
He said, "Do you know where the washroom is?"
Really?!?! That's the best you could come up with? You knocked on a complete stranger's door, then walked away because you wanted to know where the washroom is?
I finally started to clue in. Just after the knock, one of my more difficult students asked to go to the washroom. Apparently, the light knock and walk away was a subtle signal to this guy to come out and wander the halls with friends.
So, I let my student go. Then I followed him.
Sure enough he met up with the knocker and another guy at the other end of the hall. I stood watching while they completed complicated handshake/fist pumps. Then one of them noticed me. They made a big show of trying to find the washroom and disappeared inside.
New classroom rule: Use the washroom during break because no one is leaving the room on class time anymore.