Oh ok, that's interesting.  I always thought it meant butt regardless of where it's said.

First off, it's hilarious that this website would censor the word F anny, that's great!  Also to Thouze, since hogaburger provided barely any information about why Danny Trejo is wearing a f anny pack and says 'an internet video where someone dressed that way'  and is giving you absolutely zero to go on, i'll explain it to you.  It's based on the Epic Beard Man incident on the AC Transit bus and the video is on YouTube.  The real guy is named Tom Bruso aka Tom Slick aka Epic Beard Man after the fight happened.

http://en.wikipedia.org/wiki/Epic_Beard_Man

Seriously, why is he wearing a f***ypack? As if the tagline wasn't any better.