I once took a flight where I wad sitting in the second row of coach. When I got to my seat, I found that the two suits in the first row had filled the overheads with their luggage, and in addition had crammed additional stuff under their seats. I could not even put my feet under the seat in front of me, let alone stow my backpack there (which would not fit in the overhead because of their crap. ). I asked them to take the stuff out from under the seat, but they told me no "because we don't have a seat in front of us to put our stuff under". I told them that was the consequence of sitting on the bulkhead, and they needed to love their stuff. They refused, so I called the FA. She told thencto take their stuff from under the seat. Since they'd stuffed the bins and there was no where to put it, they had to check one of their bags. Karma is a bitch.