Quote Originally Posted by riskyone View Post
'Clear as mud' is both a simile and an idiom. It's a simile because it uses 'as', it's an idiom because it's a common phrase. 'Clear as a brick wall' is a simile but not an idiom, because it's not a standard speech pattern, even though the comparison it's making is basically the same thing. (simile, sarcasm, ironic, oxymoron) Unclear; difficult or impossible to understand or interpret.
Oh, dear god. We're getting English ("Language Arts") lessons now...