Packed tube this morning, I was holding on to the vertical rail at the end of a row of seats. As the seated person on the end got up to leave the tube and I waited to let them past, a woman reached behind me to place her bag on the newly vacated seat, thereby ensuring that no one would sit on it until she could make her way round to take it. As a London resident for over a decade I'm not sure I've seen such entitled tube behaviour before, but AIBU to think that you can't do this?!