If I Can't Say It, I Don't Like It
Have we covered "assuage" and "hitherto" as most hated words? Turns out, I was pronouncing them wrong for years -- more like decades -- 'cuz my only exposure was in the printed word. I did get some funny looks.
I should also bring up Audi and Acura. I bought the former when they were first introduced in the US of A in 1971 and referred to the car as an "AWE-dee." Took at least a year to get the right pronunciation, which I believe is "OW-dee." Similarly, I bought the first of several Acuras in 1988. Had the darnedest time getting that word right too. Kept saying "ah-CURE-ah," instead of "ACK-you-rah." Now that I think about it, maybe I am still saying these words wrong, although I like the words (and cars) just fine.