1. a girl bummer is a guy who always seems overly friendly and accommodating to women. He gives the impression of being the friendliest guy in the world but actually is trying it on with every girl in sight in the most underhanded of ways. He is usually despised by his peers for this behavior due to the great amount of attention he recieves from girls who just think he's a friendly guy. Under his warm exterior lies the heart of sleaze monster.
2. The other kind of girl bummer or GB really is a nice guy but is so accomodating to every woman that any manhood he had shrivels and dies.
Girl 1:"hey tom's here!!"
The Girls:"HEY TOM!!!"
Tom:"Hello ladies how are you?"
The guys:"Girl bummer!! Your a fucking GB go home!!
GB!! GB!! GB!! GB!! GB!! GB!! GB!!