Ever flown next to someone incredibly large? One of the kids and I were supposed to be seated next to two such women, side by side, on the way home from Canada. They had the middle armrests up and still overflowed into our seat, up to maybe six inches. I marched straight to the flight attendant and we were reseated. Of course, I'm impinging on other people by flying with a child on my lap. Anyway, here's some discussion of it (via terrapin on Metafilter).