Was about to say this myself before I saw your comment. I'm 6ft 1 in (185 cm) and I stand up as soon as we land because after 2 hours of having my knees jammed up against the seat in front, I want relief. I can only imagine how much worse it is for taller people. For shorter people who do this I will also give the benefit of the doubt because most seats on planes are not the most comfortable.