“Hell if I know” (I asked too many questions).
“You’re a pretty fart smeller” (smart feller in case anybody was wondering)
“Six of one, a half dozen of the other” - basically one thing is the same as the other - from my friends dad.
“Hey! Take it easy on that <equipment*>. We can fix you for free, but it’d cost money to (fix|replace) that!”
Sad part is (A) I can’t actually fix my kids for free, since insurance has copays nowadays, and (B) the “fix you for free” part seems non-sequitur, other than the implication of “go ahead, bash your brains out, but leave the expensive hardware alone”.
And yet I still do it. I hope in an ironic fashion, but probably not. 
*Canonical example is “bicycle”. Doing ramp jumps. Yeah, Dad also wanted to make sure we didn’t damage the plywood and bricks we were using for the ramp. 
And I’ll be damned if I didn’t say exactly the same nonsensical thing in the same situation to my own sons.
My father died when I was 10. I’m now 46, and father of a 5-year-old, and I find myself using expressions he used – pretty amazing how they lodged in my brain, laying dormant, all these years. Some are funny names for famous people or places – Marlon Branflakes; Pass-the-junk Avenue; Sure-kill Crawl-way (yes, he had lived in Philly). Others are fixed responses to something the child says: *hay is for horses *(in response to “Hey!”); buttons on balloons (in response to “So?” – as in, “sew buttons on balloons, and they pop”).
It’s likely my son will do the same thing I did, so he could be using expressions in the year 2040 that were current around 1950!
ETA: Also, like Chefguy, don’t just sit there like a bump on a log. My wife uses this now, too.
“Cool it with the boom booms!” as a way to get us to stop messing around. Courtesy of Ghoulardi.
“How many syllables, Mario?” if you get tripped up mid-sentence. Courtesy of Putney Swope.
“Be beacule!” (no idea of spelling) instead of “be careful.” No idea where this is from.
We say this stuff to my nieces, and dad still is around so he says it too.
Summer days are deemed “hotter than Dutch love” by my mother, who also claims that people not moving quickly enough are “slower than molasses in January.” If it’s raining hard, she says it’s “coming down pitchforks and hammer handles.” Something which is ridiculously wrong is “baloney, baloney, spumoni.”
My dad often found use for the phrase “herd of turtles”, as defined by the Urban Dictionary (right down to the “slow moving idiots” qualification).
It was often adapted to describe any annoying slow process or person.
My Pennsylvania Dutch grandmother was a good resource for phrases that I occasionally use. She used to call us shitepokes when she didn’t approve of whatever we were doing at the time. I found out later that it translated to shit-bags. :eek: Other expressions that she’d use were bugshite and “raining pitch forks and barn shovels.”
My hillbilly granny used “all over hell and half of Georgia” to mean all over the place, as do I occasionally.
Tiddlywinks is a game played with plastic discs. You use a big one and apply pressure to flip the smaller ones into a cup. Easier to picturethan to describe. So you can see that playing with manhole covers would be challenging. (You know what manhole covers are, right?)
I had a grade school teacher who had a couple of profanity substitutes to use in class. “Cheese & rice!” for “Jesus Christ,” and “Shhhhh…ugar doughnuts!” instead of “Shit!”
And the ever popular, “Hotter than the hinges of Hades.”
A friend used to say, “Useless as tits on a boar hog.” And speaking of bosoms, there’s, “Colder than a witch’s teat.”
“He (or she) who has no head, has feet” from my mother. Meaning that if you forgot something somewhere or something like that you shouldn’t whine and start walking back to get it.
“You make a better door than you do a window”, meaning “I can’t see through you”. Used most often when dad was trying to watch TV.
In response to a kid whining “I’m tired of standing here”, dad would say “Well, sit on your fist and lean back on your thumb”.
To my grandparents, a heavy rain was a “frog strangler”.
My grandfather, when crossing a road on foot, always told the kids “Stop! Look for cars, listen for horses and smell for elephants”.
“Open both doors, you’ll get cross-ventilation.”
Aargh.
Both of these from my dad:
Waiting forever to cross a street, or merge into traffic if driving, because the cars are just … far … enough … apart so you can’t go: “All in a row like Brown’s * cows!” If the delay is particular exasperating, the * becomes a bloody, or f’ing, or the like.
If someone’s being particularly melodramatic, a mocking “God save the healers, said Kitty O’Hare!” I’ve only used that one a handful of times with family.
Still don’t know who either Brown or Kitty O’Hare was, and alas I can’t ask Dad anymore.
When we used to argue with my father when we were kids, any time we made a legitimate point, he’d say “You have a point. But if you keep your hat on, nobody will notice.”
I say that to my kids sometimes just to confuse them.
Not my mom, but an aunt that watched me while I was a kid. When something was so broken that it couldn’t be fixed, she’d say “that’s seen the green weenie”
I’ve been known to use all the following…but sparingly
My father would people that did something stupid a Flipnose. But he mostly called the dog that.
He would also say “Does your face hurt? It’s killing me”
and if I was ever being loud as a kid I was “Gerald McBoing Boing”
My mother, around this time of year would sing: “Spring has sprung, the grass is riz, I wonder where the birdies is”
Both parents, whenever they said “Not anymore” would say it as Peter Sellers (as Clouseau after he destroyed the Priceless Steinway)
My cousin, who believed when we were little kids, that he could get around getting in trouble by using different words…instead of saying Penis he would call it his “Pennis Balls”
Hmmm…I would like to know more about this weenie.
My evil dad had little patience for complainers. After enduring some, he’d say, “So, what are you going to do about it?” He meant if you have no solution, I don’t want to hear about it.
Picture it, the Summer Olympics 2002. I’m living in a volunteer community and our coordinator is the most cheerful sweet nun ever. We’re watching and she is rooting for one particular male diver. He goofs up his dive and does a rather spectacular belly flop. “OhJesusMaryandJoseph!” flew out of her mouth she was so shocked! 
Another of Mom’s – describing herself as “peckish”.
That’s great!
I do this too, but I got it from Wallace and Gromit. And I do a bad Wallace impression when I say it.
I have to physically stop myself from retorting, whenever my kids explain to me what they want, “And people in Hell want ice water!”, like my Dad used to. Also usually successfully stifled is “Stop crying or I’ll give you something to cry about!”. Thanks Dad.