Inappropriate is an understatement. Selfish and inconsiderate is more like it. Why do some people think they can "prevent" other passengers from sitting next to them? I see this a lot (people putting their belongings on the seat or area next to them) and it doesn't matter whether it's on a train, plane or bus. I think it's extremely selfish. Sure, I'd love it if nobody sat next to me (in the middle seat), or even in my row, but I wouldn't try and stop them sitting where they want to.