I was flying in Business from Zurich to the US this past October, and when i boarded the plane i found a woman sitting in my seat ( her husband next to me), i asked nicely for her to move and then she asked if i can switch with her, her seat was 1st row( i hate 1st rows), i nicely declined and said that i have picked my seat months in advance and i am sorry i cannot sit in the 1st row. I really don't like it when people just sit in your seat without permission so they can just force the issue. I also suggested that her husband can try to switch with the person next to her and see if that works, it did, the person next to her was happy to not sit close to the toilet.