Imagine, if you will, that you are lying in bed, in the comfort and privacy of your own room, enjoying yourself quite thoroughly whilst images of your middle-school music teacher, your girlfriend, her fictional twin sister, an office chair, and an economy-sized vat of banana pudding dance through your head. As you lay there, tapping the natural reserves, you start to get so comfortable that you actually start to nod off a bit, not really sleeping, but getting drowsy.
Somehow, through the haze of near-sleep, you continue using the manual fuel pump. You hear nothing out of the ordinary. Everything is right with the world. And then, suddenly, you get the urge to stretch. You extend the arm currently not being used to play the organic slide-whistle above your head. Your actual head tilts upwards and to the side, giving you a perfect view of your door.
And standing in the doorway is your father, wearing a look of exquisite disgust and horror.
He's yelling, and you get the impression that he's been yelling for quite some time, but you somehow didn't hear him. Suddenly the entire world consists of that screaming man, your hands, and your pants, which you are frantically trying to pull back up but, in the absence of your legs, this cannot be done. Your father has at this point had the decency to close the door, but you can tell that he's still on the other side. As your pants finally begin to get the idea and reluctantly move towards your crotch, you shout something barely coherent about having the common sense to knock first, and then it all goes black.
You come to a minute later, peeking through a crack in your door and asking him what he wanted in the first place. You're using words and phrases you don't usually associate with speaking to your father, but he doesn't seem to care or even notice as he answers your question.
Nothing. He wanted nothing. He just had a sudden feeling that he should engage you in conversation.
He saw no reason to respect the implications of a closed door.