Tankie's original use was for British communists who supported Soviet military expansion. In the modern sense, it is used to describe communists who are authoritarian-apologists. For example, a communist who romanticizes the Soviet Union or makes excuses for the Uyghur genocide is a tankie. I've also seen it stretched to include militant anti-capitalists, or more commonly, "militant," anti-capitalists who call for violent resistance to capitalism from the safety of a keyboard.
Democratic-Socialists are not tankies. Socialists are not tankies. I don't even think most communists qualify as tankies. Criticizing Democrats does not make you a tankie. Condemning Israel's human rights violations does not make you a tankie. Voting third party doesn't make you a tankie. I see this term used here every day, but never correctly.
Not a thing about what they said is even remotely fascist. Being “put in one’s place” is an older term for what you’d know as being “called out.” In other words, they’re glad the socialists of lemmy are finally being called out for their ridiculous rhetoric.
Lasty, even if they did say shit about POC, that would be RACIST, not FASCIST.
Considering that you yourself claimed to not even know what it means, you probably shouldn’t be judging others for what they say until you learn what what they’re saying means.