The ability to detect transfolk, especially when the identified person is passing. Generally one tunes in to anatomical cues such as hand structure, brow ridge, adam's apple, and hips.
A: Wow, she is gorgeous. Look at those lips...
B: Look at those hands! Girl is setting off my trans-dar. Are you sure you're ok with that?
A: Why not? She is really something. And besides, I have a few things to learn.
A person who sees gender as a sociocultural construction and not something innate. Because genders are roles we play, and not something inherant, gender is something that can be turned on or off, tuned in or out and will. Because of this, someone who bends gender might wear baggy pants and pee standing one day, and crack out heels and a corset the next. People can bend gender in many ways and contexts, and because of this, people who are of any gender or sexual orientation can be gender-benders.
Sometimes, I feel sexy in a slinky dress and lipstick. Sometimes I feel handsome in a button down and tie. Sometimes I wear ties with skirts, corsets and cufflinks. I am a gender-bender, and I can bend gender norms to fit my conception of who I am.