With over 1 Million air miles just on one carrier I have seen some stuff on an airplane.
Sat in a 3 seat row once and the guy next to me sat in two of the seats. (the airlines have a seatbelt connector for these folks)
Seen more than one guy PUKE from too much booze
Crying kids, been next to a few and YES they can make you want to hit the exit door at 37,000 feet, especially me, never had kids. But I tolerated it for the hours I was on the plane.
In this case, the mother stood up in the aisle with the kid, walking him for most of the flight. It was when she had to sit down for landing and the plane began the descent that the kid started screaming, something common in very young children, its hurts them...I remember well my first flight in late 1948 or 1949 from Wash DC to to NYC. It hurt, bad and in those days the only thing you got was gum to chew.
It was the descent that triggered the pain in the young child. I personally would have a talk with mom as to why she did BITCH SLAP the MoFo that hit her son so hard the man's dog would think he was kicked.