Anyone who uses the term "tankie" unironically to disparage other leftists is a lib. Anyone who uses the term ironically to make fun of those who don't is a leftist. But you're right, conservatives don't know what it means, they also don't know that they are libs as well.
Your second and third sentence are true. I have definitely seen plenty of shills though.
In my experience I've only seen the word tankie be used by leftists. Libs and conservatives don't even know what a tankie is.
Anyone who uses the term "tankie" unironically to disparage other leftists is a lib. Anyone who uses the term ironically to make fun of those who don't is a leftist. But you're right, conservatives don't know what it means, they also don't know that they are libs as well.