Modern advice columns are questionable in terms of content, but Real Simple magazine's Modern Manners has a good answer or two in every issue. Catherine Newman doesn't shy away from the hard answer, when necessary shining the spotlight on redefining the problem, instead of just providing a proper etiquette solution. For August, her answer regarding a theatre experience with "a man who happened to be very large...spread out into my seat and also fidgeted" was spot on. The questioner asked how she should have handled this without embarrassing the man.
It sounds as if you were frustrated that your long awaited experience was less than ideally comfortable. That was surely true for your neighbor as well.... To quote the brilliant writer and fat-acceptance advocate Lindy West: 'If you think fat people are 'the problem' (and not, say, airlines hoping to squeeze out an extra $200 million a year in revenue, or consumers who want cheap airline tickets without sacrificing amenities), you are penalizing a significant number of human beings emotionally and financially for a disease or disability that already complicates their lives.' In other words, your seatmate could do nothing about his size and the theater's lack of space. And you should have done nothing but muster some compassion. What was a three-hour one-off for you is a daily occurrence for him - and in a culture that makes it very uncomfortable, in every way, to be fat. You could have spoken with the manager about seat reassignment or written a letter to the theater explaining the trouble with its seating and how that undermined the show. But, really, it's a difficult world, and we can only do our best to ease each other's passage through it.
What an eloquent response and a reminder to us all in so many situations.