I don’t have nearly as many personal idioms as Leonard and Sumana, or leastways I don’t think I do, but some of them have baffled people.
Have fun!
Like Sumana, I say this when people are departing to do something not normally considered fun, like grocery shopping. However, I believe I got it from Pam (whose mother says it too), rather than from Sumana.
Hot plate of X
Means “Way too much X” or “Oh no, X”. Never used when X is a desirable item. Also never used when X is a tangible item. Borrowed from an old friend; I believe the original was “Hot plate of useless.”
I’m turning into a pumpkin
“I’m exhausted”, or “I need to leave soon.” I also say “I will turn into a pumpkin at (time)” to warn people that I will be leaving at a particular time.
A Cinderella reference, naturally. I used to think I was the only person who said this, but it turns out that my grandmother says it too.
I think we all know what consciousness is
Pam and I say this when someone has just skimmed blithely past a major unresolved scientific or philosophical question. We’re quoting someone who said it without a trace of irony, during a discussion on a cognitive science mailing list.
No worries
From Australian English by way of Brother stage banter; means “You’re welcome” or “No apology is required.” I have never been to Australia.
Say again?
I have trouble hearing people over background noise. I use this bit of military/aviator jargon instead of “Huh?” or “What?”, because it unambiguously expresses “I didn’t hear what you said” rather than “I didn’t understand what you said.”
The (highway number)
This is, as far as I am aware, the only Southern California-ism that I have failed to eradicate from my speech. The Pacific Northwest convention of saying only the number just sounds wrong to me.
The thing my aunt gave me that I don’t know what it is
I never say this verbatim, but I use this construction (“that” or “which” followed by a complete sentence) all the time, contra typical English usage. I think I got it from the object with a very similar name in the Hitchhiker’s Guide text adventure.
Who shuffled this mess?
When playing cards, means “This hand is so terrible that I don’t believe the deck was shuffled properly.” By extension, can be used to complain about any sort of bad luck.
From my grandmother, who would often say it and then go on to win the round anyway. For maximum humor, say it when you shuffled the mess in question.