tankie = stalinist/maoist style communist, take control of everything, anyone who resists, run them over with tanks.

lemmy.ml has a bunch, also hexbear and especially lemmygrad.

They seem like angsty tweens who suddenly realized they figured out the solution to everything, and anyone who doesn't listen to them must be dealt with.

It's a term that goes back to the cold war. There was a strike and the Soviet Union ended it violently by rolling tanks into the city. This put communists all over the world into a bit of a dilemma: on one side of the conflict was the working class making their opinion known (a communist value) and on the other the Soviet Union (the good guys). So whose side should they take?

It was British communists who coined the term "tankie" for those who defended the SUs actions to brand them as "fake communists" who are more interested in identity politics (the good guys did it, therefore it's OK) than the plight of the working class.

Tankie is a sort of derogatory term for people who whitewash and cover up the horrors of communism.

There was a rebellion in the Soviet Union. The SU responded by rolling tanks into town and violently busting it. This put two sides of communism at odds; On one hand, there was the plight of the working class (the rebellion) and then on the other there were the actions of the people in control (the tanks). Tankies are the “communism has only ever helped people, you’re just listening to capitalist propaganda” folks who decided to side with the tanks, instead of siding with the working class. It’s sort of like calling someone a fake communist, [insert “No True Scotsman fallacy” argument from a tankie below], because a “real” communist would side with the working class.

You see it a lot on Lemmy because many instances have some major communist lean. After all, the “anyone can run their own instance and be in charge. No centralized instances, if you don’t like the mods you can just change instances” concept of the Fediverse jives very well with communist ideals. For instance, the “ml” in lemmy.ml is meant to stand for “Maoist/Leninist”. And that means the entire communist spectrum is on display; From both the more moderate “yeah communism has some cool parts but was also responsible for some major humanitarian crises” to the more extreme “those crises [were caused by individuals, not by the political system]/[never actually happened at all. They’re lies made up by capitalists to deter people from supporting communism!] Communism never actually hurt anyone.”