Harlem shake and most internet memes.
People who change the music in my car. This is meant to be an unwritten law - you don't change the music in anyone else's car no matter how bad it is. I usually don't mention this when it happens to me because I don't want to be rude, but I'm steaming inside.
People who go on about how random they are.
People who always mention their homosexuality to fish for attention and then simultaneously complain that the world even notices gay people as different to the norm.
The amount of bias in the news*. Also, the way the news (particularly television news) in Australia will ignore real issues (like floods in Myanmar, the war in Syria etc.) and instead run puff pieces about Miley Cyrus or whoever the flavour of the month is.
People who tailgate. If someone's tailgating me (I drive at the speed limit) I'll slow down. Screw you, I don't want to get wiped out if I crash because someone's driving too close behind me to stop. Driving 5 k's over the limit isn't going to get you there any faster mate (4 times out of 5 I'll end up next to them at the next set of traffic lights).
Anyway, I think the term "pisses me off" is a bit strong, but yeah the above stuff annoys me a little.
* Here's an example, and I'll keep this short and simplified. Tony Abbott (leader of the Liberal (conservative) party and current Opposition Leader) wants to get rid of Peter Slipper (MP who essentially betrayed the Liberal Party mid-term to become the house speaker, which helped the Prime Minister). Anyway, suddenly these sexual harassment allegations come up against Peter Slipper from one of his staff and Tony Abbott's using parliament time to call for his resignation. There are at least three days of front page stories about the Peter Slipper scandal, digitally edited pictures that give him whiskers like a rat etc. in the most widely-read newspaper we have. A while later, it comes out that the staff member who made the allegations is associated with the a Liberal party guy who wants Slipper's seat at the next election. Peter Slipper is found to be innocent and the judge condemns Tony Abbott for abusing the judicial system for political gain - forget sexual harassment, THIS is a political scandal. This same newspaper places this story in the corner of page 17. No front page coverage.
The television shows Q&A and The Project seem to have some bias towards the left (which is also annoying, despite me being a bit of a lefty) but they don't have anywhere near as much of an influence on the Australian public.