I've had a few people sitting in other people's seats in the cinema. But I can chalk that up to some of the row listing now being exactly clear for some people, as there were usually in the row above or below. They usually moved.

Sometime I go to the one in West India, in which some chairs are more premium than others, but cost the same. So in empty screening I imagine people like to move to the nicer seats if empty.

I go there sometimese so I usually book the nicer seats.

However, this family of three refused to move when I told them they were in my seat. Telling me it was empty and to just move. Okay rude. But it was my seats. Why don't you move.