Any person that comes to the party, asks for beer, and then takes it from your fridge against your wishes. Beer mooches are known to invite people you don't know to the party, and will also give them your beer. Any beer mooch's promises to monetarily reimburse you later should be disregarded, as they are typically full of shit to begin with.
Me: Dude, Chuck took beer from my fridge at the barbecue yesterday, after I told him not to! Then he invited over some fuckers I didn't know and gave them my beer!
Jack: Wow, what a fucking beer mooch.