If you're a germ-o-phobe you'll probably sympathize with me.  If this was my mug and I forgot it on the back of the toilet... I couldn't wash it enough.  I'd throw it away.  Guess I have a mental hurdle for a public (work) restroom and a coffee mug.  My mind/inner monologue immediately goes to "germs...GERMS... BACTERIA!!"

 

 

Notice the cup is empty (and our "high quality" TP...haha)