I'm really irritated by excessive noise.
Every day here at the school we're blasted nearly nonstop with announcements (mostly useless, redundant or repeated) over the PA system. This is irritating as hell when you're trying to help out a student, talk with a colleague or just concentrate and get stuff done, which is damn near impossible when you have someone screaming in your ear for such-and-such a person to come to the main office.
Students — especially Grade 9s and 10s, and especially girls — also seem to have this weird habit of talking to each other, at point-blank range, by either screaming or squealing or yelling pretty much as loudly as they can. I can't figure it out (and neither could my Grade 11s, who I asked about this phenomenon yesterday).
Now multiply the screaming girls by about 20 or 30, stick them in a three-metre-wide hallway, add in a squawking PA every 15 seconds, plus all the noise I get from all of my classes (some of which are very, shall we say, "lively") and it's basically an 8:30-to-4:00 nonstop barrage of noise, all day, every day.
I think I'm going to start wearing earplugs to work.