Calling someone a tartar means to call them a person of irritable or violent temper.
A person who is a tarter has a violent temper or an irritable temper.
Tatar, also spelled Tartar also any member of several Turkic-speaking peoples that collectively numbered more than 5 million in the late 20th century and lived mainly in west-central Russia along the central course of the Volga River and its tributary, the Kama, and thence east to the Ural Mountains.
If you describe someone in a position of authority, as a tartar, you mean that they are fierce, bad-tempered, and strict.
A Tartar in this context is someone who is domineering, bossy, overbearing.
It's a Britishism and quite old.
An example of calling someone a tarter would be.
A a rather large and masculine woman who wears slutty clothes usually reserved for attractive smaller women and possesses a very large penis.
If you describe someone, especially a woman in a position of authority, as a tartar, you mean that they are fierce, bad-tempered, and strict.
Or for example you might call your mom a tartar when she has a violent temper against you when you get into trouble or do something you're not supposed to do.
An example sentence of calling someone a tartar would be.
When I came home last night after being out drinking my mother was such a tartar and went into a rage and I got the spanking of my life and yelling of my life from her so that I would never do that again.