I am usually a pretty mellow and tolerant person, but there are a few things that I encounter when out in public that I find really annoying:
People taking pictures of themselves at concerts
This is the thing that pisses me off the most. You are in a dark venue and getting blinded by flashes because people are so conceited that they feel they have to take pictures of themselves in the crowd. Who on earth is going to look good in a picture taken in a dark room? The worst are those people who do this while a band is playing.
This seems to be a particular issue here in Melbourne. I constantly encounter groups of people who walk four abreast on a sidewalk. The problems you encounter are either a) trying to get around them or b) when you are walking in the opposite direction and no one moves! It's like a game of chicken. News flash people- sidewalks are just like roads. You only walk on one side of them. I'd love these people to try this behavior in New York City. They would be mowed down in less than a minute.
Riding bikes on sidewalks
Besides people who can't walk properly on sidewalks, the other group you have to avoid is bike riders. When there is a gigantic bike lane on the road I really don't think you need to ride on the sidewalk. You don't see me walking in the bike lane.
Inability to ride escalators correctly
There is a certain escalator etiquette at the train station: if you are standing you keep to the left side so people can walk up on the right. Most people are good about that, but I often encounter people who wait to start walking until the escalator is at the very top and meeting the floor. It's like they are afraid to walk once the steps flatten out. If you are unfortunate enough to be standing behind them you almost end up running into them. The escalator is not going to break if you start walking on it. I won't even get into the people I saw one day who were sitting on the escalator steps as it was going down. How lazy can you get?