Bag
As is 'ass bag'.  One of a group of friends that does no work when hitting on women, then sneaks in behind your back to steal her while you are getting a drink, going to the bathroom, etc.  'The bag' uses all means at his disposal to hate on you, as his actions are more out of sport and spite then scoring.
Mick - "Hey where did that girl I was hiting on go?... And where is Andy?"

Colin - "They're both upstairs.  What do you expect, he is a bag."