Usage is similar to that of the Golfer's "fore". After having thrown say, a steel ball bearing the size of a grape at your workmate across the factory floor, it is a courtesy to give a loud and clear "YEP!" before they are hit.
An adjective used to describe something that's garbage, terrible, stupid, or generally bad. Originates from the "yep" you say when you're being short with someone and want to piss them off/end the conversation early because nothing else needs to be said.
John: Did you finish The Last of Us 2?
Mike: Yeah, it had some fucking yep writing