Pepper Imogene...

Pepper Imogene is not just an ordinary cow.  Oh, no!  She is the famous interrupting cow! 

Pepper Imogene:  Knock, Knock.

You:  Who's there?

Pepper Imogene:  Interrupting Cow!

You:  Interrupting MOOOOOooooooo! Cow who?...
You:  Dang Interrupting Cow!

Pepper Imogene:  Who? MOOOOooo?

My son told me this Knock, Knock joke when he was in elementary school and it's so corny, it's hilarious..... In my family, if you interrupt someone - we all go "MOOOOOoooo!"