"Knock Knock - Betty" joke

Knock Knock
Who's there!
Betty!
Betty who?
Betty ya don't know who this is! Knock Knock
Who's there!
Betty!
Betty who?
Betty does'nt know who I am! Knock Knock
Who's there!
Betty!
Betty who?
Betty buy Birds Eye! Knock Knock
Who's there!
Betty!
Betty who?
Betty-bye! Knock Knock
Who's there!
Betty!
Betty who?
Betty things to do than stand here, you know!