It was a long time ago and it's late so you get the one I remember best. This guy was older, and "a little technical" in the most dangerous way. He wanted to use his work laptop for personal browsing while he was on holiday, and he thought if he replaced the boot drive with a personal drive, he could get around all the group policy lockdowns.

Unfortunately our laptops had a security module, which would blow a fuse if you tried to boot with unrecognised hardware, and prevent the system from functioning until my team could service it and replace the board. He panicked when he put the official drive back in and it still didn't work, so he took it apart the rest of the way and started looking for the problem with a voltmeter. Eventually, he thought he'd found the problem fuse, found a local electrical hobby shop that carried an equivalent, and tried to replace it with a soldering iron.

When he brought it in, he tried to play dumb, but nothing he was saying was adding up. He told me the whole story after I wouldn't take his answers at face value and kept pushing for more details. If he hadn't, I don't think I'd have figured it all out. I didn't think he even had access to a torx-head screwdriver...