Slang for "not true".

Commonly used as a defensive response or an exclamation of denial

Defensive response

Person A: "You're an egg, ow"
Person B: "Not even ow!, You're an egg"
Person A: "Whatever dick!  Not even!  You're an egg!"

... and so on and so on.

Exclamation of denial

Person A: "Hey bro, you reckon Jane likes me?"
Person B: "Not even, bro! She thinks you're an egg!"