The Septum Ring Theory is the social observation and slang that finds a pattern between women who wear septum piercing and a certain set of personality traits like being chronically online and holding exaggerated leftist views. It’s frequently used as an insult in comments of sexist / misandrist women who try to disguise their hate as “wokeness” or social justice. There’s an alternative definition that was later created by people that felt called out by this slang that claims it’s the theory that some men dislike women with septum piercing because you need to be over 18 to legally obtain it. Yeah I can see why the theory in the OP came about if it was used to attack women in this way before.