The ability to masturbate with either hand. Alternatively, the ability to switch hit in the five knuckle shuffle.
Guy 1: I burned my right hand pretty bad yesterday.
Guy 2: That sucks man, guess you won't be spanking it for a while.
Guy 1: Nah dude, I can still do it with my left hand. I'm ambifapstrous.
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi