Suckers sitting on your seat on flights

Whats up with that? I usually try to go in last so that I dont have to fight to get into the plane but by murphys law, 60% of the time, someone's already sitting on my seat. Its always they misread what's on their boarding pass, or they're just ignorant. The fact that they face humilation when I tell them they can't read for nuts just don't sink into their mind. Just today when I boarded the flight from Kuala Lumpur to Kuching, someone was sitting in my 5F seat on the 737-400. The guy had a 5D on the ticket and if you noticed, the seating plan definitely says that D is the furthest away from the window....

Damn fool!