I've got a problem with the below idiom/slang.

Spoiled rock star asks a question to her mother, then he gets mad at her and says:

"Cut you out of the equation, you old bag."

What does Cut you out of the equation' means?

(You old bag' means 'ugly old woman' ------- it's ok)

Thanks in advance
"to cut someone out of the equation" means to prevent them from participating in or benefiting from some activity, endeavour or situation. It could also simply mean stop seeing them or communicating with them. It has to be interpreted within the context of what's going on in the storyline.

"Cut you out of the equation"-

as rightly perceived, in all interpersonal dealings it is customary to assume a measure of confidentiality and trust in the discourse and when there is a 'threat' to the harmony of concordant viewpoints one could assert the intent to keep the other out of the equation for the nonce to balance the dilemma of dissent.