Excrement and slime resulting from mating dogs. As an insult, referring to somebody or something, existing at that social or hierarchal level.
"I can reduce you to dog fuck in about two minutes."
A person who engages in the act of "dog fucking" or "fucking the dog", or an instance of said activity.
"John's having another smoke break"
"What a useless dog fuck"
"Who knows? Having a good dog fuck, I'll bet"