Once, when I was on my way to class, my coffee slipped and spilled on the floor in a hallway. So I went to a restroom, got a bunch of paper towels, and cleaned up my mess.

I recall a proffesor commenting to me that it was so nice to see someone actually cleaning up after themselves.

My pet-peeve at work (since I don't have to deal with dental floss and spit ) are the items left and the copiers and printers that are shared. People have been known to print out sensitive materials (like employee evaluations) and just leave them there for anyone to see.