That part which lies precisely between an asshole and a load of shit. By extension, applies as well to persons in this position.
Originally coined by the torrent site meganova.org as a response to a legalese letter asking the takedown of links to leaked email archive of anti-p2p company MediaDefender.
Dearest little asstunnels, Let me start off by thanking you for your pitiful attempt to have your e-mails removed from the entire internet... But fair is fair you guys did suffer over the past week so here's bit of advice to you guys: F*** you! F*** you again! F*** you again and again and again! (Original Meganova posting)
I'm guessing that an "asstunnel" is what you get when a European whose first language isn't English tries to say "asshole." It seemed awkward when I first read the response, but the expression has since grown on me. (Ryan Paul, Ars Technica)