The Koch brothers. Although I know it's actually pronounced "coke" I always intentionally say "cock". I don't care if it's juvenile, it's fitting.

I say ass-par-A-guss for asparagus.
Free-sha-va-ka-doo for Fresh Avovado.
Garbagio (with an over done Italian accent - with love) for Garbage.
I purposely transleted into French: Dealer Avec (pronounced Deal-eh Av-ek) for "deal with it"
(Few other purposely poor french translations too)
And I now say 'sportsing' to refer to any sort of sporting activity. Used in a derogatory manner. As in "Them guys are sportsing and the guy on the TV says they're sportsing real good."

Be careful now because the same idiots who really pronounce things that way, once they see the smart girl does it too will believe it's correct! Like the dummies that think "Walla!" is correct instead of Voila"

Mostly to mirror something my boys say. They all had and in the case my 4 year old, still have a speech pattern where they pronounce a Th in the middle of the word as a V sound. eeeever vs Either for example. Not necessarily a mispronunciation but my now 12 year was playing with his trains one evening and would make one train run into another and then shout “Idiot!” And then look at use and go “nevermind”. He wasn’t allowed to use that word or call people that so i guess by adding the nevermind to the end he felt it canceled it out or something. Lol. We still say “nevermind” after saying things like that.

My mom still calls weeping willows sobbing willows from when I couldn't remember what they were called. I always cut the ends off of business names... Chick Fil A is Chicks, PDQ is PDs, Tijuana Flats is Juanas. Who knows how that got started...

Non-ploosed instead of non-plussed.
An old roommate of mine mispronounced it in front of me once.
It stuck, and is now an inside joke.

Almost never.

Maybe I'm just a curmudgeon, but not doing so is my one little effort to help preserve the integrity of the language. I was raised to view proper use of language as a marker of education and being willing to put in the work to get it right, especially if you came from a disadvantage background.

There are few things more off-putting than speaking with an adult who, in trying to do these cutesy words, lapses into adult baby talk. Not for me........

I view language as one giant toy.

Skissors (scissors) - my whole family has done this jokingly as long as I can remember.

Elelator (elevator) - Baby Plucky on Tiny Toons

Commerskals (commercials), sodies (any kind of soft drink), kibby/kibbies (any feline/s) - Picked them up from my ex. Also said in jest. He liked to start mock arguments about words like "fiery," (he'd say "fear-y" just to mess with me).

I get nervous sometimes because I say them automatically now and I'm afraid people might think I'm serious! ?

Anti-Que for Antique. It's the wrong pronunciation for the correct spelling.

Rural Nebraska German immigrants always pronounce Creek as CRICK. When I want to wig my daughters out, I say crick just to let them stew.

What gets my goat is when someone says Warshington, or warsh machine. There is no R in wash! One of my kids' teachers in Washington State always said WARSH. And I am thinking "why are you teaching children, especially mine?"

At work, we have a Mi-Fi (pronounced with a long i in both syllables). I supervise some ladies who are bi-lingual and English is their second language. In Spanish, i makes the long e sound (ee). The very first time they referred to it, they pronounced it "mee-fee." So I started calling it mee-fee thinking that was the correct pronunciation. They thought it was funny so I still call it mee-fee to make them smile.

I havent but could see the fun in it

I have a tendency to use partially made up words or goobledgook

such as
"My kneecaperies have got the woblesomeness"
"I feeling discomknockerated in my confusifiederation"
" If you want to give up smoking you have fagerettelessness"
"My wife is bucketfullified with Uberbabeness"

Much more bester

I tend to put a breathy "H" in front of all words beginning with "W"...Hwhat...Hwhere...I had no idea I was doing it...I now use "Wot" a lot to compensate...I do try to pronounce words correctly, but woos stir shir still is my #1 downfall...so I just say Lea & Perrins...I think as long as you know you are doing it, it is a quirky part of you and I love that in people.

Remember telling a little one:
Say eucalyptus!
He answered back: Icalyptus.

My son and I pronounce probably as prolly. Don't know why; we just do.

There are a lot of words that I prefer the UK pronounciation over the American one.

I don't do this myself, but I find it a little quirky and love it!

Depends on who is doing it, it annoys me. Maybe some bad experience from childhood - I don't know. But my best friend is foreign and he gets a lot of American phrases confused and I don't correct him because it always makes me smile. Like we'll be talking on the phone and I'll say I feel upset and he'll say 'you don't looks upset,' (he's not looking at me!) Or he'll say 'I didn't get a customer until now' and I'll say 'thank goodness you finally got a customer, and he'll say 'I just told you I didn't get a customer until now. I have no customers!'

And when I was told my kid needed speech therapy I almost declined because I thought it was adorable when he lisped.

Idiots aglore - referring to all other drivers

the ghost is queer (the coast is clear)

'Oh my Glob!' instead of 'oh my God!', ripped from Adventure Time.
'Ri-di-ci-lis' instead of 'ridiculous'.
Every now and the, 'Aack-tually' instead of 'actually', just to stress that it doesn't actually matter and I know it that it doesn't matter, but I'm saying it anyway

My grandfather used to do it all the time. Can't remember which ones though.

Not a mispronunciation so much as a malapropism, but I've always liked "Even a broken squirrel is right twice a day."