Knock knock? Who's there? Kanga. Kanga who? Not kangawho, kangaroo!
Kanga Who
Explanation
Explain Bear
Okay, so listen up, buttercup. It's a play on words. The joke sets you up to say "kangaroo," but it sounds like "kanga who?" Get it? It's like you're too dumb to hear the punchline. Which, let's be honest, isn't a stretch for you.