A combination of a banana (an Asian who is yellow on the outside and white on the inside) and a slut. Banana slugs are Asian girls who try too hard to prove that they aren't a school-girl stereotype, thus confusing being white with being promiscuous. In addition to their hooched up outfits, they often have a combination of badly dyed yellow-brown hair, fake eyelashes, dark tans, and pretend to speak no language but English.
"Did you hook-up with that hot Asian from the bar?"
"Yeah, it was easy, turned out she was a banana slug who wants to prove herself and punish her daddy at the same time."