Generally, I am more bothered by nervous people than bulky ones. I only had one very unpleasant POS experience and that was on AA and one of the events that drove me into the arms of UA.

I had the window seat on a TATL flight and the very aggressive looking POS lady could not fit in the seat next to me. She demanded that the armrest be lifted and I outright refused, mainly because it deemed to me that I could not possibly survive for 10 hours in such a position. Seconds later she was back with an FA who ordered me to lift the armrest. I declined as this it being 'unsafe for my health'. The FA ultimately demanded me to comply or being removed from the flight.
I was still too green to know about the FAs' powers and snidely said "you give me that in written and show me the rule which says that I have to lift my armrest for takeoff".

The FA stomped away and minutes later they uged the POS. What a happy ending to an ugly start .