One woman short of being gay is a term that closeted gay male husbands say to their straight wives so they can stay in a marriage of convenience.
Or sometimes the straight wives will tell this to everyone else about their marriage to deny that they are married to a closeted gay man who wants nothing but a marriage of convenience for appearance sake to appear "straight".
Belle is married to Bill and Bill is a closeted gay man, Belle likes to tell everyone that Bill is one woman short of being gay because he's in a marriage of convenience with him.
Heteroflexible is just another term for being bisexual that people who are closeted about their sexuality and want to hold onto some part of a heterosexual identity that never was there in the first place since they are not straight or hetero at all.
If the person was really heterosexual or straight they would not be having sex with the same gender while drunk or at all, or sexually attracted to both genders or bisexual.
I'm heteroflexible it means I'm bisexual but I can call myself by a different label to avoid the biphobia that gay men and lesbians have towards bisexuals.