Ever been around teenagers? I at least was one once, I'd have expected you were one too. Teenagers do dumb and bizarre things (I'm not EVEN gonna name MY list). This was hardly an act of great complexity requiring creative depravity to come to. This one can be done just by not thinking.
I was a teen ager, I'm raising a teenager, and I've coached teenagers (swim coach, ages 5 to 18).
You are correct, teenagers are often foolish. That's why we can't allow the adults who are supposed to supervise them to be be idiots at best, and in this case, propbably worse.