I absolutely hate train travel for this reason. I get that if the seat is reserved from a particular station and you haven't reached it yet and are ready to get up, fair enough, but the route I go on fairly regularly it happens to me almost every time - I book a seat and someone's sitting in it. I triple check always that I have the right seat but it's always so awkward to ask them to move as often they seem to get huffy or try to dispute it! They often also seem to scatter their things everywhere which makes me think they're just hoping the person won't turn up or will feel bad when they see they're looking so settled in.
This morning, I honestly couldn't be bothered for the scene as the woman in my booked seat had stuff everywhere and seemed to be asleep to boot, so now I'm just stood up feeling all annoyed. I hate confrontation and just can't be bothered for it first thing in the morning.
If I see a seat is reserved, I don't sit on it - why oh why do people do this??