Psychic Residue

Ever had one of those moments where you do something stupid, like drop your toothbrush on a super-grungy gas station's restroom floor? Now, everyone knows how dirty those floors are, so obviously you are grossed out by the thought of putting that toothbrush in your mouth. You turn a sink on so that you can wash your toothbrush off, but an odd phenomena occurs. No matter how much you wash and sanitize that toothbrush, the thought of it landing in some odd puddle on the restroom floor prevails. Ten minutes of washing later, you know that there's no way it could still be dirty, yet the thought of it being there makes you completely refuse to put it in your mouth. Eventually, you get a new toothbrush.
This phenomena is that of Psychic Residue, where the mere thought of something being dirty or used makes you think that it is actually filthy. No matter on what concious level you may know that you've washed something to the point that it is squeaky clean, the imagined filthyness prevails.
This also applies to the percieved grossness of using someone else's personal items. For instance, you may be spending the night at a friends house, and forgotton a change of clothes. You have no clean underwear. Your friend (who wears the exact same brand and type of underwear as you) offers to lend you a pair. Naturally, you'd be reluctant to wear another person's underwear. Despite the fact that you intellectually understand that his underwear is clean, the psychic residue prevails.