First published in a newspaper in 1934 with this joke:

Knock, knock!
Who's there?
Rufus.
Rufus who?
Rufus the most important part of your house.

The knock knock joke has been around for quite some time. And bad jokes are one of my favorite things maybe in the world. So let me get to the cream filling of this Oreo and give you the bad yet oh so good jokes.

Knock Knock
Who's there?
Interrupting dyslexic cow
Interrupting dysle-
OMO!

Knock knock.
Who's there?
Yoda lady.
Yoda lady who?
I didn't know you could yodel!

Knock Knock
Who's there?
Doorbell repair man.
Doorbell repair man who?
Every fucking time...

Knock Knock.
Who's There?
The.
The Who?
YEAAAAAAAAAAAAAAAHHHHH!!!

Knock knock.
Who's there?
I eat map.
I eat map who?
Oh god, that's disgusting!

Knock-Knock.
Who's there?
To.
To who?
To whom.

Knock knock.
Who's there?
You know.
You-Know-Wh-
AVADA KEDAVRA!

So, what do you think?