Mine is so petty but for some reason it still annoys me. The way some people pronounce the name of a certain popular candy containing chocolate and peanut butter. Reese's. Notice the apostrophe? Apparently a lot of people don't.

See for some reason people pronounce it "reese-ees" instead of the correct "reese-ez".
See, Reese's were invented by a guy named H.B. Reese, hense they are "Reese's" candies. See this cheesy '80s TV ad:
Not enough proof for you? Then take their spin-off candy, Reese's Pieces. They were named as such because the two words rhyme. It's what they call a play on words.
I argue these points with people who are close to me, and they still deny that their pronunciation is improper, even after the overwhelming evidence. Fricken stubborn people I say.
So in closing, I think whoever came up with the "reese-ees" pronunciation should never be allowed to eat "reese-ees" ever again. Also, he should be shot in the throat. Just sayin.
What's your weirdest pet peeve? I wanna see some fucked up rants here.