There are times when certain kind of behavior in public from other people really pisses me off. I've observed them here in India (I've not been out of India till now anyway ;) ). Still, it's quite possible that some of the below mentioned gestures are true for some country or even universally. And, some of these are mainly 'practised' by people who are not very educated than by those who are rather sophisticated.
(1) Many people still haven't learnt to use words like 'excuse me' or 'sorry', or even 'thank you' for that matter. They won't even say 'sorry' when it's highly expected. Just smiling or even trying to show that you ignore it at the time when you've put your foot on another person's in a bus or train simply isn't enough. I've seen instances where people even don't feel the need of thanking a person who stands up from his seat and offers it to some lady or an older person. These are very fundamental things. You've got to be courteous at least when you're in a public place. Period.
(2) Most of us need to learn basic cellphone etiquette. This is one of the most prevalent and equally irritating gestures from people. I don't think I need to go into much detail here.
One equally irritating and highly unwelcome practice followed by quite a few people (mostly those who're not very 'sophisticated', again sometimes though, I've seen so-called 'sophisticated' people doing this) is playing songs aloud while traveling by a public transport vehicle. I believe I'm quite tolerant and easy-going. But, constant bombarding of music to my ears without my expressed will really pisses me off.
(3) This one is common among people of all class. You won't often see someone throwing wrappers of piper-mint or a pack of biscuits in a dustbin. Okay, accepted that in India, dustbins aren't seen at all the places. But, in such case, you can always carry those wrappers with you and throw in dustbin later. It's not that difficult. I do that.
(4) People are probably at their worst when it comes to using public transport like State Transport buses and the general unreserved coaches of trains. In the race of getting a seat (or sometimes, getting a better seat i.e. near window et al), people simply forget, or rather don't care that it's the people who want to get down should have the first turn. People quite often just rush in and that creates a mess.
I'd like to mention here that people in the local trains in Mumbai almost always follow the rule of allowing the commuters to alight first as far as traveling by local trains is concerned (unless you're slower than expected in getting down at the right time).
(5) I don't understand why some people unnecessarily blow horns even when they are in a serious traffic jam and/or when they know that it is not going to give them a chance to reach their destination earlier. Often the same people complain about rising level of noise pollution.
(6) I've seen this in Mumbai and I guess it mainly applies here only (or to a certain extent in other metros and smaller cities). Pedestrians don't use footpath even when they've an option to. Okay, sometimes the footpath is partially (or even fully) occupied by vendors and shop owners (which is again a big-time nuisance). But, often there is enough space on footpath that they can walk more comfortably than on the road. Why do they add to the traffic on the road?