I've never had much of a problem with large people. Mostly, it's some men who are a pain in the ass, and usually it's not butt space but leg space. Some guys need to sit with their knees in different time zones and there's a battle for territory. I've gotten a bit better at winning. Most people get creeped out if the other person doesn't flinch from contact and they give you the space.

Having to deal with some guy's salami would be a little too much though.