Idiomatically challenged

I have admitted before in this forum that I am idiomatically challenged. The fallout of this being that I have a fundamental problem stringing together even the most basic idiom. Yet, I have enough of a fascination for idiomatic expression that I dogmatically insist on peppering my daily conversations with its attempted (ie erroneous) usage. A typical example of what would come out of my mouth, for instance, is 'people in glass houses should be doing as the Romans do' or something equally ludicrous.

So I was particularly proud a few weeks ago when I came up with an idiom of my own (although it must be noted there was remarkably little appreciation of my genius by my audience).

Danby, Seagull, Schaffs and I were grabbing a bite to eat in a Boken cafe towards the end of a long evening out. "I wonder what the opposite of 'A pot calling the kettle black' is," Seagull mused. There was a moment of silence as we all pondered this conundrum.
Then, "I know! I know!" I shouted excitedly. Three pairs of curious eyes turned to stare at me. "How about 'A shark calling the beach white'?!"

There was a moment of silence, which I took to indicate general awe of my sheer genius.

Then, a chorus of:
"How exactly is that the opposite?"
"What if the shark is grey?"
"What if the beach isn't white?"
"How are the shark and the beach similar really?"
"How does that even work??!!"
I was flabbergasted.

Since then I've come up with the Idiot-Proof Idiom Plan. The key is to use half the idiom, and then trail off for the second half. So in (usually) appropriate situations, I've taken to saying, "You know, when in Rome..." or "You know, people in glass houses..." and just trailing off during with a sufficient roll of the eyes.

This has two benefits:
(a) It reduces the risk of messing up the second half (e.g. 'people in glass houses should do as the Romans do'). Although there is always the risk of messing up the first half, which would be pretty shitty luck;
(b) If you use just the right expression on your face (e.g. rolling your eyes), you can convey the assumption that it is such a common idiom that of course everyone knows the second half so there's just no need to say it. That reduces (but doesn't eliminate) the risk of the listener questioning how the phrase actually ends.

I figured it to be a generally foolproof strategy. Until I hit the hurdle of uni-clausal idioms. Like 'no stone left unturned' or 'pulling teeth'. You'd assume that because they're so short it should be easy to get them right. So you'd assume. So I assumed anyway.

Until yesterday when I was having a bit of a debate with Macklaine, and I thought his points were particularly weak. "Well that's like pulling out teeth, Macklaine," I gave a triumphant smirk.
He paused. "Errr... like clutching at straws you mean?"

Dammit. So not only do I need to remember the idiom but also when to use them. Sigh. Life is such an uphill struggle.