Here are a few irritations that come to mind:
-On MSN, when you start a conversation with someone and they don't reply. You give it 10/15 mins and still no reply. Really, REALLY ticks me off. If your busy, then say your busy, I don't mind that. If your away from your laptop/PC then signout. Don't just say nothing, it's rude.
-People who chew loudly.
-Facebook whores who add pics everyday. Pointless.
-Loud TV adverts. I even put the volume on 1, and you can still hear the adverts from far away.
-Flies, Wasps, Bees.
-Buying shoes. I'm size 12, so I usually have to ask "Do you have this in size 12" They say "Ok, we'll check for you", 5 mins later they come back with the same old "Sorry we only go up to 11"
-Last but not least, Katie Price. Not for her looks (I'd still bang her) but the fact she's plastered all over the papers, TV and magazines all the time.