Made me think - I'm a bit OCD about letting anyone play my bass. Think its stems from a good friend who can kill a set of strings dead after playing it for 10 mins. He has really clammy hands and I just hate playing an instrument he's used. (He uses Elixirs for this reason!) Also don't mind oily marks from my use, but hate to see instruments clarted up (Yorkshire term) that have not been kept even moderately clean. Television highlights this too.
(Just to clarify, I'm not a cleaning freak per se, but like to see stuff looked after, especially on stage where it's most important.)