Took me way too long to realise that colonel is pronounced like kernel. Even while writing this very post I had to fact check it in the dictionary to make sure I'm not posting it wrong like a fool. Like, c'mon... there's THREE vowels in the word... three vowels three syllables! What the heck!

epitome

I thought "chattel" as in "chattel slavery" had French pronunciation, like "sha :tel," partly because the term was never really taught to me in any US history classes despite its importance in understanding historical modes of production and the particular brutality of slavery during that period.

It was quite embarrassing and cemented in my mind that, when I see an unusual-looking word in text, I should look up the pronunciation to avoid feeling like a dummy.

mischievous

I've studied a lot of dead languages, so I have a very unique problem where my brain will randomly use one or another pronunciation set on a new word. It produces some strange results.

Caveat

Vice in the expression vice versa has to be pronounced in Latin, not as in vice, I have a vice.