Along with several of the above, I use heckelopter for helicopter, flutterby for butterfly, and “do you stand under me?” for “do you understand me?” Most people just ignore it.
I know it’s pretty strange behavior for a grammar Nazi.
Untill I read this thread I didn’t realize how many freakin (my pronunciation of fucking) words I purposly mispronounce. At least half on this list.
Agreed, which is why it’s also “MINE-strone”.
I don’t have time to read ALL these posts but.
I love saying nucular instead on nuclear to the uninformed. I also say “num-nums” to my cat for treats, but again that’s my cat.
Fragile: fra-GEE-lay, vis-a-vis the dad in A Christmas Story.
Pigeon: PIG-ee-on.
Knight: ka-NIG-it, vis-a-vis the French guards in Monty Python and the Holy Grail
I like to pronounce “fajita” with a long I, 'cause then it sounds like “vagina,” and I `am five years old on the inside…
The one I use almost daily is “fitty” for “fifty”. Being uber-white, Mr. Armadillo and I find this terribly amusing. Also, frag-ile (fragile) and strategery, which is not really a mispronunciation so much as a non-word. I think it’s a fake Bush-ism from SNL or something.
My favorite is “underella” for umbrella - a friend’s young son called it that many years ago, and I’ve been using it ever since. 
I’m also one of the many “Tar-zhay” people, apparently. And while I shouldn’t admit to this, I also like “tookenen,” which I probably first heard used by the Beaver on “Leave it to Beaver,” and use it too frequently in place of taken.
Now my Dad is a huge “malapropism” person - I can’t even repeat some of his favorite ones, because they’re … er, inappropriate is probably the best word to describe them! 
And now, all I can think of as examples are those. Geeze! You’ll have to take my word for it - he does it all the time, most he makes up on his own (spoonerisms, I think they might be called?) but many others he picks up from family and friends who probably use them unknowingly. I do recall one he got that way from an older family friend who told him about a friend who’d suffered a “massy heart attack.”
I’ll come back later if I remember any printable versions my Dad uses. 
For some reason, I pronounce it Wor-chester-sha-shire sauce.
But strategery has a different meaning from strategy. “Strategery” is a word you apply to someone else’s bad strategy, especially when they think they’re being Terribly Clever, or it can also be applied to your own half-assed, spur-of-the-moment strategy ideas.
My college roomate and I used to do corn-fused, too, until one day we switched to saying “All my/his/their maize has grown together,” which garnered us a lot of strange looks.
My family uses a lot of my (German) dad’s mispronounciations: pee-yama for pyjamas, Willich Inn for Village Inn, chogurt for yogurt, Veed Vacker for Weed Whacker . . .
Oh, and nagivator.
I do this too. In fact, my whole family does it.
I also pronounce “chihuahua” phonetically: CHI-Hoowah-Hoowah. A veterinarian I worked with years ago pronounced it like that and it’s stuck with me ever since.
I’ve also taken to calling “Waffle House” “Der Waffle House” but that’s more because of my undying love for “Dead Like Me” than any compulsion to misprounce it.
ExActibly!
I can’t beleive, knowing how many Simpson’s fans must be here, no one
has mentioned …
“chow-dah” for chowder
My best friend doesn’t intentionally mispronounce these words, she is just unable, for some reason or another, to say them correctly. But I think it’s hilarious, so I always mispronounce them with her.
salsa = sa-la-sa
Mitsubishi = mister boo shi
A lot of the ones that I do have already been mentioned I think. Physic, physo, or psycho for psychic; instead of ESP we say ESPN; aks instead of ask; pasketti, matoes, and speaking with funny accents.
Shouldn’t that be “swave and a boutonniere”? 
And I always want to say “heli-chop-ter” when one passes over.
Yose-a-mite park.
(slightly off topic: Home Despot and Office Despot)
Brian
Because kilometer is abbreviated km, I call it kitten-mitten.
My husband buys electronic stuff at Suck It Silly.