Rape bait is any kind of super sparkily or glittery dress or blouse worn by girls with either a very short dress or skirt of any kind. The shiny aspect is like a shiny fish lure and instead of worm or squid for bait the girl wearing the outfit is the bait. Wearing heals (especially anything over 3.5") or hoop earnings makes the girl more susceptible just like adding bright colors and feathers to a fish lure make the bait more enticing.
Look at that rape bait across the street. I'm surpising she's made it this far coming all the way from that BU party.