Slight drift but obese pax in exit rows depends on the country. In Australia (CASA rules) you cannot deny someone the exit just because they 'look' obese. If they can use a regular seatbelt then you can't refuse them, only if they need/request an extension.
Obviously if I was uncomfortable with them sitting there I'd find another reason to move them.. but legally, you can't deny someone coz they're chubby round the middle...
If it was up to me, you would be allowed to deny them when they have to lift their guts to unfasten a seatbelt but Oz is very PC these days...
Plus to the original poster, if the CC deviate in any way and an accident happens, people die, yada yada yada.... if they didn't follow SOP then their ass is fair game in a civil court for pax's families to sue for negligence/criminal negligence/manslaughter (take your pic)