Knock-Knock ...

So, I was talking to my roommate today and the subject of telling jokes came up. I decided to really wow her with the few standard "knock-knock" jokes that I possess. Take this little gem, for example:

Knock-knock.
-Who's there?
Banana.
-Banana who?
Knock-knock.
-Who's there?
Banana.
-Banana who?!
Knock-knock.
-Who's THERE?!
Orange.
- .... Orange who?
Orange you glad I didn't say banana again?!

... and everybody laughs because it's a lame pun. However, my roommate speaks basically no English and doesn't know what a knock-knock joke is, so before I even got started I had to explain the form. Like so:

ME: See, I say "knock-knock", and you ask "who's there?", then I say (some answer), and you say "(some answer) who?", and then I say something funny.
ROOMIE: But why would I say "(some answer) who?" You just told me who it was.
ME: Well .... uhm ... you just have to. For the joke.
ROOMIE: *not understanding face*
ME: just say it.

So I tried the banana joke and after the first "banana who?" I could see she had no more patience, so I rushed to the "orange you glad" punch line. What I didn't count on was that my lame pun does not translate into German, at least not without a fifteen word explanation. So what came out as my punchline was "ORANGE - which means 'orange' in German but sounds very similar to our English word for 'are not' - you glad I didn't say banana again?! Waka waka waka! ..... It's FUNNY!!" Fail. She did not understand. So I tried this one:

Knock-Knock.
-Who's there?
Impatient cow?
-Impatient co--
MOO!!

That stuff is hilarious. But I told her the joke and it went more like this:

Knock-knock.
-Who is there?
Impatient cow (which I poorly translate into German).
-*laughter*
No, that's not the joke.
-But the cow is impatient and knocking on the door. It will not wait for me to answer.
Uhm, yes .... that was the punchline.

Are there no knock-knock jokes in the German language? Or maybe there are, and I just chose some very un-funny English ones. Maybe my delivery was off. Who knows? But the entire situation was an example of two cultures meeting, awkwardly attempting to understand one another, and then finally just giving up and parting ways. Orange you glad I told you that story?