A few years back I went to leave work and was greeted by a flat tyre, flatter than flat infact. So I went about changing the flat for my space saver and nipped down to the local tyre place.
Somehow, in between changing the wheel over and getting back in the car, I had either misplaced the locking nut key or left it in the locking nut itself... Either way, ended up with a missing key and having to have the nuts smashed off and replaced.
But here is the kick in the teeth. The tyre didn't even have a puncture, it was holding all the air that had been pumped into it and had no leaks under inspection.