Rather it's better to point out that tankies are absolutely vindicated by history because we've seen what counterrevolutions look like in Indonesia, Chile, and Korea.
If they squirm around with "actually tankie means that you support AUTHORITARIAN states like RUZZIA", it just gives you more opportunities to dunk on them for lying about what MLs actually believe, and for implicitly supporting NATO by pointing at what every single place NATO has defensively bombed looked like before and after.
Of course, always remember the person calling you a tankie doesn't actually care about the content of your arguments. You're not trying to change that person's view, you're trying to show everyone else how bloodthirsty and ignorant they are.
It's a reference to the Soviet tanks rolling into Hungary, and later Czechoslovakia, and the Western lefties (originally, the CPGB) who did not get disillusioned by the authoritarianism of the USSR at that time.
You could call us some term for Czechs or Hungarians, or Trots. At least those of us who stand by the Czechoslovak Soviet and Hungarian Soviet’s rights to independent self determination within communism.