Look at the character: 不 (not) stacked on top of 好 (good) — literally "not good." One of the few Chinese characters whose meaning you can read straight off its components. Mostly heard in northern dialects (esp. Shandong/Henan).
register
Colloquial/dialectal, mildly insulting. The compound 孬种 (nāozhǒng, "coward") is the most common form you'll hear, especially in films and northern speech.
