As the other tankie poster mentioned, it is a very old term, from the 50s and 60s, when the Soviets sent tanks in to crush Hungarians and Czechoslovakians for wanting to be a slightly different kind of Communist than the kind of Communist the Soviet Union wanted them to be. 'Tankie' was the term used by many Western Communists to condemn the Soviets and their supporters, and many Western leftists subsequently split from Soviet sympathies after the incidents. Tankies are the kind of people who say 'Left Unity' but by 'Left Unity' mean 'Everyone agrees with us or gets shot'. They're cretins, authoritarians, and usually genocide deniers, when they aren't busy celebrating genocide.