I am with OP.
I just take the seat and watch the hysteria ensue.. Loads of fun
My favorite was several years ago. "Grandma" boards first and proceeds to block out about three rows with coats, bags etc...
Flyers come on and some of the start taking "Grandma's" seats. She goes crying to the FA about how her "kids" will have to sit away from her etc.. FA does nothing (and while Grandma is off crying she lost another row.)
Just before the door closes the "kids" saunter on. NONE of them were under 21 and all of them had been happily sitting in the bar having "one last beer" because "Grandma" was saving them a seat.
They did wind up in middle seats all over the plane and the FA basically told them to suck it up or get off LOL!
So if you try this stunt with me expect to have your bag moved. And the louder you cry and scream the less likely I am to assist you. Yes, you may think I am rude, but weren't you?