I dont need a smell test to determine if fatty is obese.
Not to hate on the overweight, but when you find you cannot wipe your own ass you should consider a diet. That should be everyone's personal limit. Can't run? Can't walk a flight of stairs? Clothes don't fit? Fine. Draw the line somewhere though, and it should be no farther out than having to use a garden hose to wash the shit off of your own ass when you take a dump.
http://www.cnn.com/2013/03/27/health/time-obesity/index.html?hpt=hp_t5
"It turns out that obesity may be detectable as a gas, thanks to organisms that inhabit our gut"
Awesome! We are one step close to having a test that can tell if you are, in fact, obese!
It is methane, which doesn't actually smell, but can be detected. However, speaking from an experience on a recent flight, obesity certainly can be smelly.