Since another airline is trying to play the seatspace card that we joked about game designs for, I will comment:
Yes, it is annoying if you have to sit next to someone too fat to fit in their seat properly, so that they squish into yours. It is also annoying to sit next to someone with broad shoulders and sharp elbows. It is also annoying to sit in front of children who keep kicking the seat, or to sit behind people who like to lean their seat back over your dinner. It is annoying to sit anywhere near a baby that screams, or someone who gets airsick (eewwww). It is *extremely* annoying to sit near someone who is ill and be stuck catching their germs in the limited airspace.
It's not even just other people who are annoying! It is annoying to sit in an economy seat if you are tall and your knees are jammed up into the seat in front of you. It is annoying to have a butt that is slightly too wide for those small seats and is getting jammed into the armrests, or stuck having hard bits under you. It is annoying if you, like me, have joint problems that mean you cannot keep your knees bent for long periods of time without great pain. It is annoying to have your feet or arms or something in the aisle in a desperate attempt to get some space and then be slammed into by a flight attendant with a heavy cart.
In short, FLYING IS NOT COMFORTABLE. It's not fair to pin the blame solely on fat people.