The term “flange”, a collective noun for baboons, has gained some currency as a serious term. It was originally used jokingly in Not the Nine O’Clock News in the famous Gerald the Gorilla sketch with Rowan Atkinson.
“Thagomizer”, the term for the bundle of spikes on the tail of a stegosaurus, was coined in a Far Side cartoon. Some serious paleontologists are now using it.
But I’ll say prolly so.
“Brobdingnagian,” “lilliputian,” and “yahoo” (meaning “fool”) – all from Gulliver’s Travels.
“Malapropism” derives from the parody figure of Mrs. Malaprop in in Richard Brinsley Sheriden’s The Rivals.
“Hoodlum” was coined as a one-time nonce word describing a particular gang, but became part of the language.
waitaminit…
I’m not sure if this counts, but in some instances of taboo avoidance (inserting a made-up word or a word that sounds similar for a “naughty” word), the euphemistic word also becomes taboo. The most famous example of this is “ass” for “arse.” People said “ass” as in donkey as a euphemism for “butt” but is now itself considered taboo. In Hungarian, the original word for “bear” was taboo (as it is in many languages; if I remember correctly, the English word “bear” was once a taboo avoidance in the distant past), so they borrowed medved, which was borrowed from some sort of Slavic. But the Slavs were using it to avoid using the taboo word for “bear;” *medved *comes from the word for “honey.”
In Britain “yob” is pretty common as meaning young hooligan (at least in Sun headlines)
it comes from the backslang (reversal) for “boy”
We had a thread about this some time back. Since the “nerd” depicted by Dr. Suess has little in common with the original meaning of the term (being an imaginary animal that looked more grouchy than geeky), and the word is mentioned as being widespread on college campuses with that meaning within a short time after Suess’s book appeared, it seems more likely to me that either 1) Suess picked up a word that was already current in the spoken language a little before its first use elsewhere, or 2) Suess’s use was coincidental.
See here for the sequence of usage:
That’s why you have “Beowulf” instead of “Bear.” “Bee-wolf” was a euphemism for the bear, which was sacred and unnameable.
Google “circumpolar bear cults.” I find this whole area fascinating–that we once had a hemisphere-girdling religion/worldview of which almost no one is aware today.
What about “truthiness?”
I’m not sure what this thread is really about. The example in the OP is “sammich”, which, as I see it, is a reasonable spelling of a mispronounced real word.
If that’s what we’re looking for, then I nominate “ekcetera” and “Febuary”.
Fred Hoyle first used the term “big bang” sarcastically when referring to a theory for the origin of the universe that he disagreed with. The theory has since become widely accepted, and the name stuck.
It’s not a “mispronunciation” except with reference to particular dialects, sociolects, and registers. In a general sense it’s simply an alternative pronunciation which actually may be the “correct” one in some cases.
“shat” and “thunk” are too words that I see bound to enter the dictionaries soon enough.
The word ampersand is not a silly parody, but it is based on a mispronunciation/conflation of “and per se and”.
The word ‘apron’ used to be ‘napron’ until enough people who heard ‘a napron’ figured it should just be ‘an apron’.
Going the other way is ‘atomy’, which I’ve only ever seen in dictionaries - it means ‘a skeleton’. It’s a joke formation from the skeletons seen in anatomy classes (‘an atomy’)
I’m hoping Pratchett’s Headology replaces the original.
What’s wrong with shat? It’s already in the OED, anyway.
“Burgle” and “snuck” are rapidly gaining ground. My spell checker still worries about “snuck” but is fine with “burgle.”
I remember being taught that only a complete degenerate would talk about burgling. Times change. 
Nother as in “that’s a whole nother story.” As much as it burns my ass, I don’t think it’s leaving us anytime soon.
Normalcy. Thanks Jimmy Carter for that abomination! However incorrect it may be, it gets uttered on the evening news all too often.
Grok. A made up “Martian” word coined by Robert Heinlen in* A Stranger In A Strange Land.* It’s becoming so pervasive that I hear people saying it who don’t even know who Heinlen is. 
Doesn’t ‘normalcy’ go all the way back to the 1920s? I seem to remember reading about the ‘Return to Normalcy’ in “Only Yesterday”, the popular history of the 1920s written in 1931.
Edit: here’s Only Yesterday in full HTML glory. Frederick Lewis Allen, 1931. And Chapter 2 is titled “Back to Normalcy”.
So it wasn’t Carter’s fault.