Tankie is an empty signifier

That is to say, it's a label that can be used to describe an array of different and conflicting ideas, values, and identities. Because of this it serves as an obfuscatory device rather than a communicative one. The sub-logic becomes tankie = bad, so if someone I don't like = tankie, then person I don't like = bad.

Almost none of us were alive when Khrushchev rolled tanks into Hungary. Most MLs aren't particularly fond of Khrushchev.

It's made a resurgence in this new, weird context because most of the terms used during the previous red scares lost their power through similar misuse. It's become unfashionable to hate on leftism in progressive spaces, doing so using old terminology makes you sound like a fox news conservative. But you can do the same thing by calling it this instead.