Liberals do use it since "commie" lost its zing. Go to any reddit thread where somebody is speaking sense and there'll be a liberal going "don't listen to him, I saw his history and he's a tankie", likewise with any Facebook thread when some blue no matter who page says something profoundly silly
I'm aware, I've just never heard/seen a liberal use the word "tankie"- though I don't often expose myself to liberals... Are libs actually using that word now? I would literally laugh out loud at the hypocrisy if I witnessed that
I've seen many I definitely don't think are Anarchists use it, and I've even seen Anarchists and Liberals get labeled "tankies." It's a generic term used like BadEmpanada is referring to, a largely meaningless catch-all for Leftists.
No, Anarcho-Capitalism is a deeply unserious ideology that doesn't even understand Capitalism well enough to understand that it can't exist at any significant length of time without a state enshrining Private Property Rights.