So many.....
People who walk whilst using their phones, I have no issue with this other than 99% of them walk at unbearably slow speeds and become completely unaware of all surroundings.
People who act like savage animals to get on the train but when faced with left or right, faff about so much I lose any chance of getting a seat.
People who can clearly see the train is busy, yet leave enough space to land a jumbo jet and need firmly instructing to move their idiot bums further down.
People who have no awareness of their surroundings in general, especially behind them and do things like immediately stop without realising what will happen.
People who lurk by entrances or stairs where it's obvious people need to get past.
People who palm off their phones or tablets to kids who are much too young to be using them, thus creating another generation of most of the above.
People who sneeze into their hands, why can't you pinch your nose?
People who think it's a good idea to leave on the keypad tones on their phones, or people who watch their mobile phone for ages deciding if they should answer it.
People who walk past mothers with prams/old people, that could do with some help (saw an old woman who could barely walk up the stairs herself at Stanmore with a bag, helped her and when i returned downstairs I saw two staff members doing absolutely nothing).
People who play music or YouTube videos without headphones.
People who queue in a normal (human operated) lane at the supermarket with barely anything in their basket (a couple of weeks ago, one banana) just because they can't be arsed to use self checkout, creating long queues.
Everyone who uses a bank or post office as they always seem to need help that requires the most amount of times.
Probably a lot more, and I'm a happy go lucky guy!
Edit - as others have said, these are moans rather than 1st world problems.