I was in the IAD-GRU flight last Wednesday which was delayed first because of the general computer glitch, then because there were 52 connecting people arrived, then 7 people gave up and they needed to remove their luggage, and 4 hours later, finally the crew time wear off, and the flight was rescheduled to Thursday 10:00am (we took off 11:00am, but it is other story)

The flight was full, I was 31D, when we received the announcement about he connection people, the couple in the bulkhead 30D & E collected their luggage and went out. Some time later, the people started to show up, and a couple of women seated at 31B & C. When the flight attendants started to close the bins, the woman in 31C jumped to 30D, and her companion moved to 31C. It was probably at 3 hour late mark, everybody was expecting to depart soon, but they didn't know yet some luggage in cargo bay was very deep inside. As I wrote before,at 4 hours mark the flight was rescheduled to 10:00am next morning, everybody got a hotel voucher.

Next morning, back to airport, I checked the app and both 30 D & E were still open, and 31 was full. I changed my seat to 30D, boarded quickly, went to my seat OK. My neighbor from row 31 boarded a little later, I turned back and started to chat with him. Some time later, the two women boarded, I was still talking to him, and he told me "there is a beg in front of you!" I replied him I had no idea what was that probably a FA put there.

Less than five minutes later, a FA shows up and asks me to put the bag in the bin (I was in the bulkhead), I told her it wasn't mine - and the women at 31C "oh, it is mine, I was seated there yesterday!" and I replied "ok, but I changed my seat to be here today"

"Like how did you change the seat?"
"Well, I changed from back to here this morning, because it was free"
"Oh, I didn't know we could do it..."

If a look could kill... I'm pretty sure she was intending to pat my shoulder when they closed the door and ask me to move because she had the open seat before...

During the flight every time she went up to screech the legs she stopped in front of me and look at me sometimes sad, sometimes upset, sometimes with rage... OK, but the seat was rightful mine now.