Extreme overreaction in my opinion, although "nega" is kind of a mispronunciation as I assume he meant 那个 (na ge).

A little related, but 不是 (bu shi) sounds like bullshit with the right pronunciation, and both phrases/words can be used in similar situations.

It's not a mispronunciation; it's a regional variation.

Well, now I know what that word I kept hearing in China was...