I caused havoc in high-school with that. And finding a way of executing binaries inside Novell's Netware thing, via the "Open" dialog within any Office application's Visual Basic macro editor haha
I created a directory with alt+255. It was an unprintable character and showed up last in any dir listing. At most it added an extra new line. That’s how I was one of the only students whose apps didn’t get caught during auditing.
However it turned out that you could rename them .bat or .cmd and they would execute just fine.
I think Doom 2 multiplayer was extra fun because of the added need to be aware not just of in-game enemies but also the need to be aware of the teacher and be ready to instantly quit at any moment.
Wrote a batch script that used a wildcard - it took them a while to find it and I was very lucky the only 3 persons who knew who it was wouldn't tell anyone.
One was a teacher and I am thankful until today that he didn't screw up my life with telling this.