Whenever my mom hears something she can’t believe, she says “Golly.” However, it’s not just pronounced “Golly,” but more of a “GollEEEEE” with the accent on the last syllable. I swear, for years I thought she was saying “Godly” 
.
My dad always used to say “colder than a witch’s tit in a brass bra” or “colder then a well-digger’s bum.” Every morning when he’d drop us off at the bus stop, he’d say goodbye with “don’t let your tits drag in the snow” (which I guess is kinda weird, now that I look back on it.) One day my sister turned around and said “don’t let your balls drag in the dust!” (He worked at a plant that makes gravel.) I don’t think I’ve ever seen my dad so shocked.
While my mother calls my father “Papa Smurf”, my father calls her “Monks” - short for “Monkey”. Because of that, my mother has a nice collection of toy monkeys; including some pretty cool Beanie Baby ones. (I like the baboon with the psychedelic ass. 
) We also have a cousin that we used to call “Monkey”. I wonder if his wife has caught on yet?
Anyhoo…
My dad has an expression that he uses when expressing consternation at, say, a slow driver: “Slower’ whale shit at the bottom of the ocean!”.
I don’t get it.
He’s also fond of the insult “dickweed” - a term he may or may not’ve made up.
My mother doesn’t have any odd sayings/expressions, but her mom always says, when expressing disbelief, “Mother’a’GOD!”. Hilarious.
Oh, yeah! My father’s fond of the expression, “Slower than cold molasses going uphill in the wintertime!”
Anyhoo…
Whenever someone would choke in my stepmother’s presence she would say, “did something go down the wrong throat?”
We have a ritual we always do when we go to the beach. If we see a rock in the sand that might be interesting enough to keep, we’ll pick it up. My Dad’ll say, “Is it a leverite?” If we decide we don’t want it after all, we’ll toss it away and say, “Yup, leave 'er right there!” My Dad thinks his Dad made that one up.
I wish I had your grandmothers 
My brother also says, “Shut the front door!”
Not because he doesn’t swear (he does), but because he’s trying to be funny. It works.
My parents used to say “Useless as tits on a boar” when I was a kid. I always thought they were saying board, and I’d imagine a pair of breasts on a see-saw. I never really “got” it… :rolleyes: