I checked it out on Merriam online, and both pronunciations are correct, but I've never heard anybody say "di-a-BEE-tees" instead of "di-a-BEE-tus." And I worked in hospitals for two years. Must be a regional thing.
Most of the others listed here bug me too.
It won't mean anything to anybody else here, but in the legal profession, at least around here, 75% of lawyers and judges say "trial in absTentia" when they mean "absentia." I usually say, "He didn't show up. Whether he had sex or not, I don't know."
MIL sometimes says "sodie" for "soda", meaning soft drink. I've learned to deal with "soda" for something not involving ice cream (I'm a "pop" guy

), but "sodie?" Drives my wife nuts in particular.
Has anyone mentioned "hopefully" yet? I think we've lost that battle, along with "nucular" - when the last five or so Presidents make the same mistake (pronunciation, not pointless invasions of tinpot dictatorships, but that too

), I think the fight's over.