A girl who will resort to promiscuous or flirtatious behaviour to get help, advice or anything else she wants from a helpless male victim. Once achieving her goals ("sucking him dry"), the penis vampire ignores the poor sod, treating him like a total stranger.
Male 1: Wow, I'm so bummed out, I thought I had a chance with Emma
Male 2: Why what happened?
Male 1: She asked me to help her study for philosophy and she was all flirty and I thought I was in but after the exam, she totally ignored me.