Knocking can be used as a very versatile word. It could mean joking, failing, messing around, fucking, etc. Meaning is up to context of the conversation.
“you look like an idiot, why you knocking?”
“bitch, are you knocking that guy?”
“girl you have to be knocking right now”
When a turn is at the pearly gates of your butthole.
"Dude I gotta shit so bad, it's knocking on heaven's door!"
When two women vigorously scissor.
“Eating a combo of oysters & chocolate always has me in the mood for knuckle knocking.”
The signature knock of a friend/family member.
That was The Bock Knock. Brenton's at the door.
Engine Connecting Rod Knock. Usually caused by excessively worn Rod Bearings. This results in an audible Knocking Sound that is pervasive and matches with your RPM of the Engine.
I was driving my Car in town and suddenly Uncle Rodney came knocking.