A person who only has sex with people who ride bikes. Alternately, a person who is turned on by bikes and bike culture, specifically in a sexual way.
Not only does that hottie at the coffee shop ride a fixie, but she's totally bikesexual. I can't wait to show her my ride!
To be attracted to only people who ride bikes or are involved in bicycle culture.
Man: "Want to get a drink sometime?"
Woman: "Do you ride a bike?"
Man: "I did when I was a kid, but now I ride a motorcycle."
Woman: "Sorry, I can't date you, I'm bikesexual."