This is whats called an meta-joke. The initial part sounds like a joke.. the audience is waiting for the punch line and it never comes - which is why its funny (in an ironic sense). Its sort of like the joke is making fun of similar jokes without actually being a joke itself. Its hard to explain, but I hope you got the gist. A few random jokes in along a similar vein.. Whats worse than finding a worm in your food? Finding two worms in your food... - An Irishman walks out of a bar.. - What's the difference between a Jew and a pizza? A Jew is a person adhering to the Jewish faith and a pizza is an oven-baked, flat, usually circular bread covered with tomato sauce and cheese with optional garnishes.

ROFLMAOMG. It's called an "anti-joke". The joke begins with a typical set-up, but the punchline is a very serious response. It's the opposite to what we expected, so we laugh. Another example of an anti-joke: "Why was six afraid of seven? It wasn't. Numbers are not sentient and thus incapable of feeling fear." The punchline we expect is, "because seven ate nine" (ie. Because 7 8 9.) www.youtube.com/watch?v=3cPs2SzShNc