“It’s raining cats and dogs.”

“He’s all washed up.”

“That’s straight from the horse’s mouth.”

At least two of those statements are always idiomatic in nature. That is, their meaning is not readily understood by the words composing them. Cats and dogs are not falling from the sky. Horses don’t speak human speech, and nothing I care much about comes directly from a horse’s mouth. (Horse saliva? Thanks, I got mine already.)

But what about “He’s all washed up” as an idiom? He could be ready to eat, and has washed his hands and face prior to coming to the table; he’s all washed up. There, it’s more of a regional speech than an idiom. The words mean (almost) what they look like they’d mean.

Now, what if he’s been given a task to complete on pain of losing his position in something (the workplace, a sports team, the HOA landscaping committee), and he’s failed to do so? We could say “he’s all washed up,” meaning “he failed,” “he’s done for” (an idiom in itself), “he’s finished” (ditto, especially if he’s washed up because he didn’t finish!).

And “I didn’t catch that” means “I didn’t hear you,” usually. Nothing’s been literally thrown, so it can’t be literally caught.