I recall someone saying the term originates somewhere online, and describes literally those who are cool with the tanks coming out and government authoritarianism, so long as the people being run over by the tanks are seen as fascist righties.
But the other comment sums it up pretty well, the lefty extremist Boogeyman is real, it’s just a tiny minority being amplified. The right don’t like 'em, the rest of us don’t like 'em either.