Not just a communist. A tankie is a person who says they like leftist policy and ideals but then go on to honor authoritarians who used leftist language to secure their power. See: leninism, maoism, all the fools constantly praising China while crapping on the US, all the fools sucking off the USSR even though it was never socialist...
They're generally immature and under-educated buffoons who think they like leftist policy but still have such a pathetically tiny understanding of authority, governance, and policy that they'll praise authoritarians in one breath and claim to actually be an anarchist in the next.