A rot twat is an incredibly unoriginal hipster girl who has a facial expression like she just licked battery acid, permenantly. She tries to screw whoever she can, whenever she can, usually standing in four inches of sweat and sludge in the men's room of a seedy, yet trendy bar.
"Did you see that girl go into the bathroom with Randy Andy?"
"Yea that girl is such a rot twat. I heard that she only showers on easter and x-mas. unless she just had sloppy drunk sex. then she waits another week."