Tankie refers to people who support authoritarian "communist" regimes and often deny or justify the atrocities they commit. Stalinists mostly, but also supporters of the authoritarian aspects of China and even North Korea
The internet's superpower is to drain words of meaning.
Initially the word Tankie was a very specific, very directed insult. It was a pejorative for like. Y'know, Soviet-Union simps. "Leftists" that spent a lot of time memorizing Soviet Union WW2 trivia and adorning themselves in Soviet ephemera, much like how certain nazi teens do. The accusation was very direct and very clear: "You do not care about the workers' cause. You just like the Soviet aesthetic and have a very weird thing for ww2". Like a Wehraboo except they'll call you 'Comrade' instead of a racial slur.
It then, by simple extension, became a pejorative for Marxist-leninists. Cuz of course. Most MLs are Soviet Union simps, later they transitioned to being China simps and would you look at that, China also offers a lot of military ephemera they can be, y'know, weird about. Of course if you lack a bit of context you can then use it for any vaguely authoritarian 'leftist' and you won't even be all that wrong, it's close enough.
Eventually though? It sorta leaked (thanks a lot, Adam Something)
... And now there's a lot of like, straight up Neoliberals using the term 'Tankie' as an insult in the same way their conservative grandparents would have used the term 'Pinko'. It has entirely exited the purview of leftist discourse.
Don’t federate with that instance if you don’t like its views.
TBH, I find even this view kind of... foreign? It makes sense to defederate from instances that cause harm to the ecosystem (whether by hosting trolls or not guarding against spam) but I just don't think that "federation" should indicate "approval" in the way so many folk clearly do. Like, letting someone on gmail email me doesn't mean I approve of what google does.
I view lemmygrad.ml as political spam and bad thoughts not worth propagating. lib.lgbt is also unfederated from sh.itjustwor.ks because they hosted a The_Donald community while wringing their hands about the free speech implications of jettisoning it.
You using gmail means you approve of what Google does. If Google started platforming alt-right content and you were fine with that, that does say something about your approval as well.
To borrow a segment from Wikipedia, Tankie specifically refers to those who might speak out in defense of the Soviet use of tanks to crush the Hungarian Revolution of 1956 and the 1968 Prague Spring uprising.
I've, on occasion spoken favorably of specific USSR policies or of specific Warsaw Pact or NATO policies without intending to show approval of militant or imperialist policies, which has gotten me accused ot being a Tankie of Atlantism and being kicked of subreddits.
Initially it was a term used to describe supporters of the Soviet union invasion of Hungary in 1956. The Soviets deployed tanks to suppress the country hence tankie.
It was then used by libertarian socialists against Marxist Leninists. Now it's mainly used by liberals to label anyone who's further to the left than them.