I'll balance on the exact edge of your emotional razor.

[Dark_Fury]

Hello. This is a piece of dialogue from American movie "Gone Girl".

Nick's wife has gone missing. She's a popular writer and there'll be a press conference today (held by the police). Nick's sister, Margo, tells him to be careful.

Margo: When you're upset, you bottle up. You can seem angry, like...
Nick: Please don't say, "Like Dad."
Margo: Or else you swing into your momma's boy charm offensive, and that can feel glib.
Nick: I'll balance on the exact edge of your emotional razor.

I was wondering if you you could explain to me what Nick means by "your emotional razor"? Does Nick mean that his sister is an emotionally balanced person, so today he'll act just like she usually does?

 

[J&K Tutoring]

He feels there is a small distinction between the "angry" his sister mentioned and the "glib". This fine line is like the sharp edge of a razor, and he is telling her he will be exactly in the middle between those two.