In combat, you do +10% damage against opponents of the opposite sex. Outside of combat, you'll sometimes have access to unique dialogue options when dealing with the opposite sex, similar to the Sex Appealtrait. In Fallout: New Vegas, it is complemented by Confirmed Bachelor perk.
You can invoke some humorous dialog between you and the Lonesome Drifter; he informs you that he lived in Montana and his father left before he was born, the player has the choice of worriedly asking "Montana? Oh god, you wouldn't happen to be 17 would you?" to which he replies in the negative, and the player responds by attempting to change the subject.