As already mentioned by others, loud eating noises grate on my nerves like little else. In the unlikely event that I ever commit murder in a fit of rage, the victim will probably be found with a mouth full of partially chewed food.
At work, I can't stand what I call telephone terrorists. You know, the people who call you up and take you hostage. Their motto: never say in two minutes, what you can say in twenty. They don't tell you what they want up front either. The worst offender in my office begins with excruciatingly long stories filled with tedious and often irrelevant details and when she finally does get to the point, she sometimes backs into it so obliquely that I often still don't know the core purpose of the call. What do you need from me? Just bloody tell me.
The vapid bleating by those of a certain political persuasion. 'Nuff said.
Junk science, pseudo-science, new age hoodoo, urban myths and legends, and all other manner of bovine fecal matter swallowed whole by people who simply couldn't be bothered to exercise a smidgen of critical thinking. Even worse, when they forward same to my inbox. Here's a clue, Sparky. It was BFM when I saw it 1, 2, 5, and 7 years ago...and it's BFM now.
Oh man, the list could go on and on. I think I'm a curmudgeon. Do they have support groups for that?