A leftist (usually online) who believes that anything that conflicts with their worldview is a "conspiracy theory". Karens are generally just fat, bitchy white women with black "husbands", so it makes sense for this word to be used to describe them in this sense. Due to "QAnon" being the left's biggest boogeyman at the moment, it is ideologically convenient to dismiss all opposing information as conspiratorial so that one does not have to waste useful brain cells trying to reflect upon one's own beliefs and self.