Boring Betty
When you interact with an attractive lass, only to realize immediately that along with her obvious good looks, she has the personality of a wet mop. Outside of outright rejection, nothing is more disappointing than approaching a woman to introduce yourself, hit on her, and find out she has the social and conversational skills of an invalid. The 'Betty" is tribute to the character from the 'Archie' comics who shared a similar disposition.
"So I saw this cute girl out and immediately after I introduced myself it was clear she was another Boring Betty - all looks, no substance."