Originally Posted by cmn.jcs

I'm understanding him to mean that while boarding, sometimes someone will seat down, then leave for the lav while placing an item (sweater, book, etc.) to show the seat is taken. Even so, he/she will still sit down and take the seat. Maybe the original person shouldn't leave, but there's still a big difference between saving a seat for someone who hasn't boarded, and saving a seat while you run to the lav. Sounds pretty rude, aggressive, and wrong.