ALL SHOULD be offended. Jumpseating is a courtesy we extend each other. DO NOT assume the seat is yours. As much as the FAA wants us all to be jointly responsible for the flight, this is MY aircraft: I signed for it, and when the chit hits the fan I will be the one they talk to. So, do me the courtesy of ASKING for a seat.

By the way, when I dead head, I still let the CA know I am on board and have a ticket. IMHO it is courtesy, and lets him know there is an able bodied crewman on board in case things go south.