You know those handheld staple removers that look like a bird's beak? Clean the freakin' thing out when you're done! Someone used mine to remove about a hundred staples, and they were somehow stacked up along the arm of the staple remover, all the way to the point where it became jammed. Yes, it's a minor thing, but someone (a) entered my office when I wasn't there, (b) used my stuff without asking and (c) rendered said stuff unusable. That's a trifecta of common courtesy violations.
If I find out who did it, their chair won't have wheels anymore.