Wife: "There's trouble with the car. It has water in the carburettor."
Husband: "Water in the carburettor? That's ridiculous."
Wife: "I tell you it's true."
Husband: "You don't even know what a carburettor is. Where's the car?"
Wife: "In the swimming pool."
Made me laugh, anyway. Thanks to the Adam Smith Institute Joke of the Day for brightening my evening!