Actions directed towards the neccessary goal of silliness. Alternatively, the profession taken up by court jesters, jokesters, joshers and the like.
Man 1: Take it easy man I was just joshing you!
Man 2: Oh, you mean to say yoou were conducting your silly business with me... That is acceptable, Alpha Niner.
The first known use was in the movie Manchester by the Sea. When asked if the nephew was sleeping with a specific girls he answered, "its just basement business", when asked more specifics he simply said I'm working on it.
So basement business is teenage monkey business usually of a sexual nature.
Have you and she had sex even though her mother is home? No it's just {basement business].
It's like telling someone - Piss off, I no longer wish to hear your voice and pretend to be interested.
-Thinking- "Man, I really want to get away from this idiot... I can't stand the prattle eminating from their mouth...."
-Speaking- "Hey, Bill... I have some business to take care of. Can I get back to you later?"
The socks you where when its business time, popularized by Flight of the Conchords.
I remove my jeans but trip over them because i still have my shoes on, but then i turn it into a sexy dance. Next thing you know I'm down to my socks. And you know when I'm down to just my socks, its time for business, that's why they call it business socks. - Jermaine