I see you've already received shitty advice by a couple of dingbat posters who have tried to turn this around into, "why are you looking into a 15 year old's bedroom?"

Ignore them. They, well, dingbats (with equally dingbat posting histories).

If some kid is jerking it in view of you, you have a couple of options. One: meet the parents and have an uncomfortable discussion. Just me, but that's probably what I'd do because option #2 has consequences for the kid and parent. Option #2 is you call the cops and say, "my neighbor's kid is jacking off facing my window."

The idiots here saying teen boys jerk off are, well, idiots. Yes, teen boys jerk off a lot. No, normal teen boys (or anyone, of any age) don't do this in a window where they can be seen.