Out-to-Lunch
Thinks s/he gets paid by the post
I'm another one that read a lot and didn't know the pronunciation of some words. I was careful to not use words I wasn't sure of pronouncing but one day decades ago at work I mangled "voluminous". I suppose this instance doesn't fit the OP's request as I hadn't mispronounced it a long time, only once, but I sure remember doing it.
"Excoriate," for me.
"Imprimatur" comes under this heading, too.