Can be used either as:
1) A profanity.
2) An insult. (Meaning bad or shitty)
3) A commonly used noun, that can replace almost all other nouns.
"Oi! Shitnitch! Gimme back my wallet!"
"That exam was such a shitnitch."
"Sup shitnitches! Lets grab a shitnitch down by that slow-shitnitch shitnitch over by the shitnitch. Aww, C'mon! Don't be such a shitnitch, shitnitches, you know ol' shitnitch here is a shitnitch."