Ah karma...it got me too, but the other way. CGD-KUL on MH flying J on an A380. I was settled into my (carefully selected in advance) seat when a FA asked me if I wouldn't mind swapping with a young man a few rows ahead so he could sit with his girlfriend who was next to me. I was in a less-than-good mood already, maybe thanks to the obnoxious check in staff at CDG. PLus, I'd done the right thing and prepared, not my fault. And why was I being asked and not the person next to him. Etc, etc.
Like a jackass, I resolutely refused. In the end a man from a few rows forward moved back to take the woman's seat next to me. Here's where karma got me: Turns out he was travelling with his family, and had voluntarily and cheerfully separated from them. Of course, his family spent the rest of the flight coming back to talk to him, using the space in front of my seat as their own personal aisle. And it was a big family!
I should have moved, it would have made no difference to me. Lesson learned.