A couple of jobs ago, I had just come back from some time off. I was sitting in my cube working when a co-worker I had never met came into my cube, reached past me, and grabbed a tissue from my tissue box without asking. If you think that's bad, it's nothing compared to what he said: "Thanks, I've been stealing these!"

I wish I were kidding.

I've had co-workers steal my and my desk-mates' gum before, too, at the same job.