Nerve/a nerve

Nerve/a nerve
 

Are they correct?

-The villain says, 'He wasted my time by answering my question, and you expect me to return discourtesy with politeness. What nerve.'

1. Are the red words idiomatic English?

2. Do you think a is required before nerve?

Both nerve and a nerve are used.

The words in red are used correctly. There is no idiomatic expression going on, though.

Excellent answers. Thank you.