On 4chan, EVERYONE is a faggot (regardless of sexuality), and a need came up to differentiate between types of faggotry. A homosexual would be a gay fag, and a fan of Japanese cartoons would be an anime fag.
I wanted him to do me up the butt, but it turns out he was a straight fag.
Straight Minus is to be straight but close to being asexual. When you are straight minus you are attracted to someone of the opposite gender, but you find the sexual human body to be strange.
Kevin: Did you hear about Juanita?
Kyle: No, what's wrong with her?
Kevin: Nothing, she's just Straight Minus