Must have been on this thread several times, but easily, hands down, the thing that irks me most in modern life is people assuming that the entire carriage/bus/shop/street/district wants to know the details of their home life or whatever and literally bawling it into their mobile phone. Oh and walking around in circles gesticulating wildly in the street, taking no notice whatsoever of whoever's trying to get past, while they're doing their bawling.
I hate mobile phones in general and only got one this year under extreme duress. Leave it at home switched off most of the time, tbh.
Edit: oh, and while we're about it. People looking at me in wide-eyed disbelief in the years when I didn't have one, saying “But how do you survive?!”