Twice in the last month I have had a overly larger person in the middle seat next to me. Both times ORD-SFO, so it was not a short flight. The person in the middle occupied about 3 inches of my seat. In one case, the person's upper body hung over the armrest. I complained to UA (email), but no response. I think this person should have been required to purchase a first class ticket.

I don't want to throw stones because I'm not a small person but I definitely can contain my body inside the limits (armrest) of my seat.

So what should I have done? The second time it happened I knew what I was in for. I thought of getting off the plane and requesting the next flight and having someone else endure the discomfort for 4+ hours.