Hmm. I'm borderline overweight/obese according to the BMI index (29.something) but the doc just laughs when I pointed that out, saying we'll be ignoring that completely in your case.. Being built like a brick has its advantages..
On topic though - I've seen morbidly obese people have difficulty driving due to gut interference with the steering wheel, making all car control a more difficult endeavour. Having to sit far enough that the wheel doesn't interfere meant that the indicators and dashboard switchgear was inaccessible. I think there's a case for taking these people off the roads as a danger to themselves and to others, and damn the PC brigade.