I was on a flight on SWA from Austin to El Paso several years ago and had someone about 350 in the middle seat. His wife was in the window seat and his fat @$$ was almost pushing me out of my isle seat. That was a flight from hell as well. He also smelled like he hadn't had a bath in a week.
Physics. Extremely obese people cannot physically reach their ass to wipe. Ever been to a fat person's house? They usually have a waterhose hooked to the bathtub to act as an improvised bidet. Some are so fat, they can't reach certain "rolls" and develop some pretty nasty fungi and bacterial infections under their fat rolls.
Same here. The first thing he did after he sat down was raise the armrest between us. “Do you mind?” he said. “Absolutely” I said, and lowered it back down.