A woman who befriends a gay male and constantly flirts with him, in hopes of getting something more.
Grace, from "Will & Grace" is such a flirt hag.
A gay guy's best female friend, who secretly hopes for the gay friend to fall in love with her. This is usually canalized through playful flirting and jokes about becoming a couple.
Grace was Will's flirt hag in the show "Will and Grace"
Guy: "Look flirt hag! stop messing with my boyfriend"