My friend little brother (he’s seven) made this one up. I’m very amused by stupid things.
Knock-knock.
Who’s there?
Christmas flower.
Christmas flower who?
(insert farting noise here)
Hehe.
Then there is the classic
Knock knock
who’s there?
interupting cow
interrup-
-moo
As long as we’re doing knock-knock jokes…
Tell someone you have the greatest joke ever. Give it a big buildup. Then say, “Wanna hear it?” They respond, “Yes!” You say, “All right, say, ‘Knock-knock’.” People are sheep, s/he will respond, “Knock-knock!” Respond, “Who’s there?” and look at them expectantly until they catch on.
Hey Max!
Are you a duck? 
ROFL Max! I’m using that one when my mom gets home from work. ::snicker:: And the duck one, too. Thanks, Falc. I’d almost forgotten that one. Hehee.
I used to have to use knock-knock jokes to get my nephew to hug me before he went to sleep at night. “Knock-Knock!” “Who’s there?” “Can I?” “Can I, who?” “Can I have a hug?” It cracked him up every single time. But I always got my goodnight hugs.
:scoff: No!
My mom, while laughing: “Those are stupid jokes.” LOL
Ok, here’s my cheesey contribution to the knock knocks…
Knock knock!
Who’s there?
Offer.
Offer who?
Offer got my key, lemme in!
groan
Anyways…
-Dani
Here’s one that no one ever gets:
Knock knock.
Who’s there?
Knock knock.
Who’s there?
Knock knock.
Who’s there?
Knock knock.
Who’s there?
Knock knock.
Who’s there?
Knock knock.
Who’s there?
Knock knock.
Who’s there?
Phillip Glass
Your right, I don’t get it.
I got it. That’s hilarious.
Ha
Ha
Ha
Ha
Ha
Ha
Ha
Ha…
(Laurie Anderson laughing for cornflakes…)
I got it! And it’s all my brother’s fault.