What's your onboard pet peeve?

When I read about an Idaho man allegedly slapping a Minneapolis toddler on a plane (and using a racial slur in the process) in an ill-conceived attempt to make the child stop crying, my mind raced. I thought of the poor babe, whose ears hurt because of the descent. I thought of the mother and her shock. I thought that whoever hits a child to make the child quiet down is pretty ignorant of child psychology and, more importantly, deserves a wallop themselves — and much more (which the courts will decide in the case of the Idaho man). But, sadly, I also thought of the times I've grown unnerved on planes, hurtling through the sky with strangers (some rude, some loud, some simply annoying). Flying can drive us all slightly mad. I wonder what onboard pet peeves you might have — and how you deal with them (without resorting to physical violence, of course). As for me, when the person next to me raises the arm rest without consulting me first, I feel like my personal space has been invaded. How do I retaliate? I merely lean a little in the opposite direction and put in my ear buds. You? I'd love to hear.