I'm still irritated about when I was a youth I found a somewhat obvious security hole, and took advantage of it in a mildly funny way, the staff just punished me.

You weren't supposed to be able to change the desktop background, but for some reason MS Paint had a "set to background" option that worked. So I set the background to a screenshot of the desktop, and then hid all the icons and start menu. Later, the teacher thought the computer was broken because "nothing was working".

I think it could've been a good teaching moment. A talk about not messing shared resources up, and channel my interests somewhere productive. Nope. Just a lecture and week long library ban. Disappointed.