The opposite of the 'midas touch'. Rather than everything one touches turning to gold, to have the 'faecal touch' means everything one touches turns to shit.
This can be applied to people who are generally incompetent or just going through a stretch of bad luck.
'How's work going at the moment mate?'
'Just awfully dude, I definitely have the faecal touch. It doesn't matter what I seem to do or how hard I try, everything I am involved with completely fucks up and turns to shit.