I see this term used so often from the lofty reaches of some national news rag or echoing out of a Senate star chamber. The CEO is stamping it into an EULA, as an irrevocable term of service. The corporate union-buster is putting it up in 120 point font in a company wide mandatory power point presentation. The evangelical minister is denouncing it from the pulpit as part of a catechism call-and-response. The nosey neighbor is whispering it into the phone, hoping a SWAT team will remove someone from the block. The police holding you face down in a bucket of water are screaming it in your ears.
Beware the authoritarian communist. Beware the tankies. Beware the Chinese / Russian / Venezuelan social terrorists, fifth columnists, and outside agitators. Beware the college kid in the Che Guevera t-shirt. Beware the Anti-American. Whatever you think we might be doing to you now, they'll be ten times worse.
Meaningless distinction. Whether it's military or whatever. Whichever state supported group is shooting and beating and arresting protestors in China, they're tankies.
You're just salty because our superior ideology beat yours into dust (this applies if you're an actual communist or just a right wing agitator pretending to be one).