One of the most difficult classes I took at the UO J-School was J-101: Grammar For Journalists. It wasn't that the content of the class was difficult, it was the sheer amount of stuff you had to learn and memorize in preparation for the LSDT, which you must pass to become a full Journalism major at the UO. So while that class totally kicked my butt (the test was far easier), I do still have a place in my heart for oddball grammar and how screwed up the English language is.
But my biggest pet peeve is when people think they are holier-than-thou, and insist on correcting your grammar when, in reality, their corrections are incorrect. There's a list of great examples here, along with a huge list of common errors in English (be sure to read the introduction here). There's even a page for folks who seem to always mis-pronounce our beloved state.
(Note: Yes, I know the grammar on this site is sometimes atrocious. I never once said I was a good grammarian.)