I was once called a tankie because I was advocating for tenant unions

Tankie is when

It's annoying when capitalists genuinely think tankie is synonymous with Marxist. There's nothing inherently wrong with being a communist or a socialist, but many people lack the education and experience to understand what separates tankies from other socialists. Much like tankies, they believe China is somehow communist, only they disagree as to whether this is a good or bad thing.

It's especially annoying because actual tankies are dangerous as hell. Some of them seem convinced they're more left wing than anarchists or libertarian socialists, despite the fact that the best existing ML states are capitalist autocracies. While alliances with tankies are possible, they will stab you in the back more consistently than liberals once they gain power. They point out how many liberals will disappoint you, but it's the case of a black hole calling the kettle black. Tankies inherently silence opposition to the party. The few MLs who do what's right will be silenced by the tankie majority.

I hate the people who misuse terms like tankie, as it gives tankies the opportunity to point at the misuse and claim the term is meaningless. Ignorant leftists believe the tankies, and repeat their lie, not knowing they serve the interests of a wannabee ruling class. That's the perverse part about all of this. The states tankies support have serious class stratification. It's an inevitable feature of those system, and tankies refuse to even consider what changes to Marxist-Leninism might prevent it. Shutting down reasonable criticism is a vice, not a virtue. It strengthens the group mechanically, but results in terrible outcomes.

The term has its uses, but as any term, it is many times used for people who don't fit the term at all

Like I'm not innocent in this, I tend to throw it around regularly, but only when arguing with people who explicitly defend authoritarian governments.