DAB is an acronym for drunk ass bitch. It is usually used to refer to a woman who drinks excessive amounts of alcohol, and proceedingly acts trashy, obnoxious, bitchy, or simply idiotic.
Oh look, Tracy just did 10 shots of Jose Cuervo, and now she's dancing on the table in only her underwear and telling everyone that she has a really bad case of crabs... such a dab.
The common dab (Limanda limanda) is an edible flatfish of the family Pleuronectidae. It is a demersal fish native to shallow seas around Northern Europe, in particular the North Sea, where it lives on sandy bottoms down to depths of about 100 metres (330 ft).
The Danish man caught quite the big dab on his trip.