...and other frequently used idioms that have lost all actual meaning.
If a stovetop pot of water is set on "5", and you stare at it--sure it would be just as boring, if not more so, than watching paint dry--why would it defy the laws of thermonuclear chemistry and not boil?
A bird in the hand is worth two in the bush. Hold on a minute. Are you telling me that during the transfer from the my hand to said bush, this bird is suddenly able to clone itself? And if that is possible, why are we not throwing everything in the bush?
You catch more flies with honey than with vinegar. I don't think either method will catch more flies, because those little buggers are fast! Sure, Ralph Macchio had beginner's ruck in Karate Kid, but don't expect that to happen twice.
People who live in glass houses should not throw stones. As Demitri Martin brings up, though, if you are trapped in a glass house, and you're holding a stone, by all means throw it. And I've always thought this saying made more sense as "People who live in glass houses should not walk around naked."
You can't judge a book by its cover. All I do is judge a book by its cover; if the cover is boring, the book is probably boring too. That's why movies have all the action in the previews. They know that if they showed the actual movie no one would see it. Instead of making this a metaphor for humans, why not just say straight-up "Don't judge a person by their appearance"?
He got up on the wrong side of the bed this morning. The only way this makes sense is if he sleeps on a balcony and rolled away from the house when he woke up. In fact, this sounds like it could be used as an opening scene of a "CSI: Miami" episode, with David Caruso uttering that horrible line, and then The Who screaming "YEEEEEAAAAAAAAAAAAAAHHHHHHHHHHH!" as the intro starts.