Approved Slang..

I can honestly say that I've never heard anyone use "rock" before as slang

However, I did hear someone use the word f'gonna once or twice... I assumed that they combined finni and gonna... hmm

's == it's or that's the listener/reader needs to understand which one it is by the surrounding context. I use that one a lot.

shiznit can be ok sometimes
dope is not ok
da bomb is not ok
smooth can be ok sometimes
slick can be ok sometimes
bust that out can be ok sometimes

It really all depends on who is saying, how often the person usually says it, the tone of voice the person uses when saying it, how popular the saying is, and the situation when the person uses for determining if a slang word is ok or not.