It was 5th period, and the high schoolers were at lunch. My group of 8th graders were watching a video, and I was watching them to make sure that they were watching said video and not doing things that might later turn into a problem. I spent much of the period shushing them.
Then I noticed a hand in the window. And then another. I should mention that the windows are up high, probably about 5'6" above the ground. So, if a hand was in the window, someone was deliberately waving it. Then I noticed someone's face peering in.
After that, one of the hands leaned against the window, and the window tilted open. Then the whole class heard some maniacal laughter. So, I got up, went to the door, and leaned out.
"What are you doing?"
I found a gaggle of boys hovering outside. Since it was their lunch, all I wanted was for them to stop antagonizing my class. The boy who had opened the window gave a very pitiful excuse--something about his hand "accidentally" leaning (the window is up high, so I doubt that his opening of the window was in any way an accident). I shoved the window closed with a thunk (the window is high, but not that high), and I closed the door.
I watched the windows closely after that, but the boys did no more after that than discuss whatever boys discuss at lunch. Though, when one girl from my class was called to the office later, I heard them comment to her that the class was dark. Well, sure it was. We were watching a video!