"Knock Knock - Butter" joke

Knock Knock!
Who's there?
Butter.
Butter who?
I butter not tell you! Knock Knock!
Who's there?
Butter.
Butter who?
Butter let me in! Knock Knock
Who's there!
Butter!
Butter who?
Butter be quick, I have to go to the bathroom! Knock Knock
Who's there!
Butter!
Butter who?
Butter bring an umbrella, it looks like it might rain!