Impact, impacted or (God help us) impactful. I used to just hate when some self-important corporate twit used them to mean effect, affected or effective. By the time it spread into general use, I just started to hate the words themselves. And impactful isn't even a word.
That can be extended to just about any perfectly good word that has been turned into corporate jargon.
Surgery. Again, I didn't hate this word until people tried to sound smart by misusing it, referring to "a surgery" instead of an operation. Which led to the even more idiotic plural, "surgeries." And to make matters worse, doctors have started saying it. To illustrate the problem, imagine someone pointing at a steel mill and saying "they do metallurgies there."
Which brings me to chiropractic. Perfectly good word, except that it appears to be the full name of this field of medicine. Every time I hear it or see it on a sign, I want to yell "chiropractic what?"
OK, that turned into words I hate on principle, rather than words that just don't feel good or sound good. But I guess they're unpleasant just the same.