I don't think you're using the term correctly. All the other stuff in this thread aside, the phrase "sense of entitlement" is typically applied to those who want to appropriate from others, not to those who want to keep what they have. No matter how boorish the folks here seem to you as they speculate on what they might do in a hypothetical situation, you can't accuse them of having a sense of entitlement for choosing to keep the seat assigned to them. If anyone has a sense of entitlement in this situation, it's the person who believes he is entitled to another person's seat.

You may believe he is entitled to the other person's seat too, but please don't accuse the person sitting there, who bought that seat and wants to keep it, of having a "sense of entitlement." No matter how noble the motives of the appropriator, or how base the motives of the possessor, the phrase "sense of entitlement" can apply only to the person who wants to take from another, not to the person who wants to keep what is his.