The most irritates things for me is noise.
Sometime too noisy, until you cannot sleep or study.

ignorance, violence and rap music

parents who don't or wont control thier kids

the little yappity dogs that live next door. They bark at everything 24/7 and their owners never tell them to shut up

O, I hate that too!!

Okay, I don't really know if this is the thing that irritates me most, but it is all I can think of at the moment.
My computer: I reckon that it is good and all, but it can become really slow, and sometimes, for example right now, my computer just freezes, for no apparent reason, and then about 5 seconds later it will go back to what I was doing. Another thing that my computer does, is sometimes, out of the blue, it will just close what i was doing. This is what probably irritates me most.

Damn, that has got to be one of the most irratating things. Really!

Dry hands or feet, nails on a chalkboard, chalk

My thing is the chalkboard and also cardboard, like closing a cardboard box, and the flaps scrape eachother.

i see how that would be irritating

People who don't know how to make a decision....or won't make decisions. Drives me nuts!!!

Unnecessary bureaucracy

narrow mindedness, it imprisons people, and they don't even know it. see it all the time.

Not being able to get to sleep at night. Some nights it seems I stay awake the whole night.

Stupidity. Traffic. Loud people. People who know better, but do it anyways, and then fuss when they have to suffer the consequences.