The ability for a person to sit and put either right OR left leg up on the other knee.
Because he was ambilegstrous, Eddie sat for 8 hours in a meeting without having to move - he has the ability to cross either of his legs, unlike most of us who can only cross one favored leg.
Since James was ambipegstrous he was able to use his friend's bike which had pegs on the left side, though he was accustomed to pegs on the right side.
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