Dumb as a box of rocks. But a box of rocks is pretty smart actually. Rocks are difficult to carry on their own; and they may have sharp edges too. Try holding an armful of rocks without a box, and I’ll supply the laughter. “Ha ha! Dropped one! On your foot! Would like something smart like a box, wouldn’t you?”
Built like a brick shithouse. Apparently an approving statement about either a man or a woman. To me, this would indicate being rough and sturdy on the outside… and full of shit on the inside. Which is, at best, a mixed compliment.
Like herding cats. This is supposed to be something difficult; something that indicates you have people that do not respond well to directions. First thing first, cats are not people, they are extradimensional beings who have mind control powers and have in secret good kitty cats are nice do not suspect the cat. Secondly, hypothetically speaking, herding cats would be easy. You just don’t use a dog (as with herding sheep), you use as a “sheepdog” some animal that cats look up to, and feel respect tinged with fear towards. I am speaking hypothetically because this animal would need to be some kind of a hyper-cat, which as far as I or you know, do good kitty cats are nice do not do not exist and there is no reason to go looking.
A leopard cannot change its spots. Sheer stupidity. Leopard only needs to use a razor… oh wait, leopards do not have opposable digits, so the Bible has a good point there. But a leopard with a human accomplice can, using a razor, remove its spots, and then use a good coat of paint to make new ones. I hope this can be included as a footnote in the next edition.
As white as snow. As a city-resident Finn, I can tell you this means “mostly white, with yellow ravines and brown drops here and there”. Source of which depends on whether the location has pets, kids or students.
Also, “as pure as the driven snow”? I have seen snow driven in trucks out of the city center. It is an ugly grey-brown sludge, and it occasionally has dead dogs in it. This saying is stupid and disgusting, and probably is some cryptoracist dogwhistle backformation which I disapprove of, “How was his new girlfriend?” — “As pure as the driven snow if you know what I mean, it’s a shame those people are allowed here.” A better phrase would be, “as pure as the clean and pure Finnish master race”, if you are a racist that is.
Pearls before swine. This apparently means something wasted. I, as a noted expert in zoology, can with sincerity and gravitas say this is not a waste. Pigs eat pearls, you see. Which is not a waste either, because pigs have a very strong metabolism, so the end result is truffles. Which are worth more than pearls so there!
Three sheets to the wind. Apparently used to mean, “very drunk”; comes from Finnish peasants who, once suitably slushed, took the Sunday bedsheets and went to pose as ghosts to scare the parson’s wife; this was a common way to pass the time because before the Internet Finland was very boring. Then there would come a strong crosswind called ithaqua, and the sheets would be in the wind, the drunk Finns would be naked, and the parson’s wife would be even more horrified and the parson would be arriving with a flintlock and the wrath of God. So in summation “three sheets to the wind” does not exactly mean “very drunk” but “in very big trouble, like with your privates about to be frozen, shot off, and/or destroyed by the wrath of the Lord God Almighty as the fig tree was destroyed”.