I don't know if it's OCD or what it is but it's certainly unpleasant to watch and he does it right in peoples' faces while he's talking to them. It's like watching a toddler with it's fist in it's mouth and nose during it's oral fixation. It's deeply unpleasant in an adult and just adds to the general air of shiftiness about him. I never trust anyone who talks from behind their hand.
Let's not even mention how after picking and scraping and peeling around his orifices he then runs it all through his hair...