Shall we discuss how for all of fifth grade I was adamant that Hermione was pronounced "Hera-myohknee?"
I even have the mini-Aragog to prove it -waves Heramione-

And I don't quite remember the assignment—might've been a five-minute persuasion thing, or something like that—but it involved me getting up in the front of people and talking, which is always a dicey prospect. On this occasion, I was explaining that words like "nuclear" and "especially" have certain correct pronunciations. For instance, "nuclear" only has one U in it; it is not "nucular." And "especially" does not have an X in it; it is not expeshully.

To make my point, I proceeded to spell out the word "especially."

And forgot how midway through. My brain blanked out on me.

Fortunately, my class was not a bunch of total jerks, so everybody just laughed (totally fair; I had to laugh, too) and we moved on. I'm prone to that kind of thing when nervous, though, so that's one reason I will never be a public speaker. {= P

~Neshomeh

It is not pronounced ep-eh-tome.

My German (mother language) teacher managed to start at positive and go over to optimistic. During the word, which resulted in posimistic. She tried two times more, and both times we ended up with posimistic.

Let's see... I used to pronounce debris as "derbys," (turns out I swap consonants a lot,) and thoroughly as "throughoutly."

Add this to my chronic misspelling of the word sandwich (it almost always shows up as sandwitch,) and a tendency to indiscriminately add or drop T's. (For example, attached =/= "attatched," which is what it sounds like it should be.)

On a much funnier note, when I started taking Spanish, there was a girl who didn't understand that orange (the fruit) and orange (the color) are different in Spanish. Therefore we one day got treated to a really pointless discussion of her weekend, where she mentioned she ate the color orange. :/ We teased her for weeks.

Around where I live, what nobody can pronounce is "Probably." We say "prolly," usually, or "probly." Why? Midwesterners are too lazy to grant a repetitive word more than two syllables.

In Arabic, the word for 'bathroom' is 'ham-mam,' so when you want to go to the bathroom, you say 'biddi roo al-hammam.' However, 'hammam' is pronounced like that because you hold the m for longer. If you don't, then you're saying 'I want to go to hell.'

...the name James Bond was somehow reduced to a mispronounced "jambon" by my father who was trying to speak in French.

It stuck to the point where my family refers to the James Bond series as ham now.

I also used to confuse "trempette" (dip as in food) with "trompette" (trumpet). I distinctly remember asking my mother for carrots with a bit of trumpets on the side when I was about seven.

Hargarine - or hard margarine. It actually made so much sense it stuck, and my parents joked it ought to go into the dictionary.

You remember this one, Specs, but I'll let everyone else know that I once confused 'tongs' with 'tonsils' while discussing how clean a donut shop worker's tongs were.

"Wow, those tonsils she was using were really clean, weren't they?"

/sobs

One memorable incident ended with a serious discussion of the half life of geraniums. Turns out they aren't radioactive after all.