Not too long ago I had the reverse of this experience when flying WN. I was sitting in my seat listening to music when an elderly woman speaking limited English boarded at the last minute, poked me on the shoulder, and then pointed to her C4 boarding pass, proclaiming "MY seat".

I took off my headphones and said "It's open seating, you can sit anywhere." Perplexed, she stood there holding her ground with about 5 people backed up behind her. Fortunately an FA saw what was going on and came over to straighten her out before the situation escalated. Had she tried to poke me a second time I might have gotten a little ornery myself. As the FA ushered her towards the rear I heard her again uttering "why he in my seat?"