Large genitalia - male (or female) REALLY do it for me. Don't know where the desire came from but I do know that it sends me crazy when I see a man with a very large penis (I am a bisexual) - I feel an overwhelming desire to be dominated by both the penis and the person and will do whatever they desire to satisfy that feeling.
I have also known a couple of women with an extremely large clitoris and they induced in me a feeling of total arousal just looking at their genitals. I can masturbate and ejaculate very quickly just by visualising large genitals of either sex.
