“Schuyler”.
If you’re referring to the work by Byron, the pronunciation is, indeed, “Don Joo-un”; this is the only pronunciation that makes the poem scan correctly. Given the work’s playful and comic tone, and its almost Ogden-Nashian approach to rhymes, I assume Byron did this deliberately rather than out of ignorance.
[QUOTE=Lord Byron]
I want a hero: an uncommon want,
When every year and month sends forth a new one,
Till, after cloying the gazettes with cant,
The age discovers he is not the true one;
Of such as these I should not care to vaunt,
I 'll therefore take our ancient friend Don Juan—
[/QUOTE]
I came in here to say this, but since it was mentioned, I’ll add one from when I was a little kid playing Zelda. I always read the game over options as Continue, Save, and “Ret-tree”. It wasn’t until I was a bit older that “re-try” finally clicked.
I used to think “debacle” was pronounced DEB-uh-cul instead of dee-BAC-ul.
The first one I really remember was Ingenue
Though my dad was always talking about the character Donkey Hotey, which I never connected with the book (pronounced Don Quicksote) that he had in his den.
Exactly what I came in here to say. I was corrected rather embarrassingly in my freshman English class in high school.
I have a friend who actually paid money to see Captain Corelli’s Mandolin in the theater. Now he hates Penelope Cruz’s guts along with anyone else who he thinks is responsible for that movie being made. He knows how to pronounce Penelope, but as an expression of disdain he calls her “Pennuh-LOW-pay”.
I used to do that. My dad said one of his smartest lecturers at university used to use it all the time too.
Hermione.
In a group in 8th grade science, I was reading aloud something about “debris” and has no clue what it was. The next person started talking about “debree” and I probably turned red.
Chaos (pronounced “chows”).
Grotesque (pronounced “gro-tes-cue”).
Elementary (pronounced “el-EM-en-tary” with the emphasis on the second syllable. My mom STILL deliberately mispronounces it this way to bug me).
Or is it apropos?
I used to mentally pronounce it “der-biss.”
biopic: I pronounced this like “bionic” (in my head. I don’t think I ever had reason to say it) until very recently.
segue: Like “fugue”
quixotic: I took Spanish in high school, and we read Don Quixote, so clearly this is pronounced Key-hote-ic. No, I guess not 
I will never forget the humiliation I felt in 8th grade.
I was to read the poem The Ancient Mariner out loud to the class.
I pronounced it "ma-REEN-er.’
Aspartame, as in the sweetener (Nutrasweet). I pronounced it “as-par-ta-may” for the longest time.
I pronounced invalid like it was two words “in valid.”
When I was about middle-school age, my mom and I were going through old newspaper clippings which included Watergate-era editorial cartoons. I knew, in general terms, what had happened, but I’d never actually heard anyone pronounce the word ‘subpoena’. When I asked my mom what a ‘sub-poe-ee-na’ was, she just about lost it laughing.
My son corrected me about “HY-purr-bowl” earlier this week and I just now learned about ennui and quixotic.
I’m never speaking aloud again.
My cow-orker loves to tell the story about how she and her husband went into KFC and how everyone at the counter, including her, were completely puzzled by his order for the Co-low-nell’s chicken special.
.