"The hell it isn't." ???
SCRIPT
Edie: "Oh come on, you're not gonna beat a girl like that by knocking off early."
Susan: "It’s not a competition."
Edie: "The hell it isn't."
Susan: "Good night, Edie."

QUESTION
I can't get it of the expression "the hell it isn't."
What would you say about this?
Thanks in advance. ^^

Question

"The hell it isn't." ???
SCRIPT
Edie: "Oh come on, you're not gonna beat a girl like that by knocking off early." 
Susan: "It’s not a competition." 
Edie: "The hell it isn't." 
Susan: "Good night, Edie."

QUESTION
I can't get it of the expression "the hell it isn't."
What would you say about this? 
Thanks in advance. ^^

Answer

It's a heated way to disagree with what has been said.  He is trying to say she is wrong.

Answer

"The hell it isn't." 
It is an expression of severe irony. Technically, he is agreeing with Susan to the point of it being so ridiculous that he means exactly the opposite.

Example:
A: China is a democracy.
B: The hell it is!