I like the phrase, “That ship has sailed.” People are always left speechless.
Only works if there’s water under the bridge.
“You’re not exactly un-digging that hole, you know.” Addressed to someone who might better have thought before he spoke and is now doing his damnedest to backpedal. Best said laconically. Not entirely meanspirited.
“It sounds like English, but I don’t understand a word you’re saying.” This has a range of applications, but be nice and don’t say it to foreigners with strange accents, and yes, that means the Scots, too.
“Shoes too tight?” Good for someone who’s throwing a snit. One of my favorites.
“I beg your pardon?” Said with slight sarcasm to let an individual know they are either incorrect, exhibiting poor manners, and/or should apologize. As an example: someone says “Shoes too tight?” and I say “I beg your pardon?” dripping with sarcasm.
If we’re talking about who I think we’re talking about, that ship has sailed.
(psst. dwest, edit your earlier comment from “boat” to “ship”. My bad.)
I shall inhale that remark.
[sniff]
Bless your heart!
(it helps to be southern US or have influences there to get the idea)
Me aul’ Da had a few.
“Bless your cotton socks!”
“Away and have a titter of wit, man dear!”
“He hasn’t the wit of a sucking turkey.”
“Never break your wind, in case you follow through.”
“It just lets you know what it shows you!”
(for me this last has transformed into)
“People who like this sort of thing will find that this is the sort of thing they like.”
“Enough to make a sailor’s trousers” - a hopeful sort of comment when the weather has been bad, but there’s a break in the clouds and you can see blue sky. It’s Cornish, or at least that’s what she told me.
“All the world’s a fool, except thee and me. And I have me doubts about thee.” - one of my father’s sayings. Self-explanatory.
“There’s nowt so queer as folk.” - another of my father’s. He was from Buxton, Derbyshire.
“Ay up, mon-kay!” - get a move on/hurry up. Another of my father’s.
One I use from a former business partner “Lies, Lies, Lies!” This originated 25 years ago, so I believe long before the song(s) and book.
My dear ol’ Dad used to use that one when someone passed gas… 
When she was little, my niece Rachel used to say “What’s the heck of that?” instead of “what the heck is that?” Our family kinda adopted that, and we use it all the time.
I had someone say that to me the other day. I’ll translate that for non-Southerners. “Bless your heart” means “You are crazy and whatever you want, it isn’t happening.” I knew what she was meaning too but I had no response because I knew she was right, so I said, “Thank you.”
First it’s slight, and then you drip. I’m not sure what you intend. And what a way to respond to a solicitous, concerned inquiry after your footly good health. Tsk. They must be too tight after all. 
I’m wearing these. They’re not too big, they’re not too tight, with the built-in air pump they fit just right…'course I had to get new socks without phalanges ventilation.
Are you really wearing those, dwest? If so, what happened? Did you injure yourself?
That too is most excellent. 
Spider barks.
I remember one fellow said “low-flying mice”, but he’d had a few.
A line I borrowed from John Steinbeck’s Grapes of Wrath, which was just on the other night. “That’s the truth to you/him/her.” Said in the right tone, this avoid conflicts.
I sometimes say “We’ll burn that bridge when we get to it.” if we are better off waiting for things to play out before deciding what to do about a potential situation.