Which preposition?

"angry with"

You can also say:
I am angry with the way she treats her boyfriend.
I am angry with her attitude.

You can also say;
I am angry at him.
I am angry at him for taking my car.

thank you for that eye opening lesson about English.

"Angry With" does sound odd. It seems ungrammatical.
However it is probably the most common way of expressing disappointment in someone's ACTION.

Saying that, "you are angry at someone" is a much more common way of saying this; if you compare it with other European languages.