Two or three times per year, an air traveler, sometimes a celebrity, will lash out at an airline for being told they do not fit comfortably into one seat and will have to purchase another. While some airlines, like Southwest, do have a policy that requires "passengers of size" who "encroach upon any part of the neighboring seat" to purchase extra seats as needed, they do not have what's come to be known as a "fat tax."
Earlier this year, former chief economist at Qantas Group floated the idea that heavy people should pay more to fly, much the same way passengers are charged more for overweight baggage. The theory is that the heavier you are, the more jet fuel the plane needs to burn to carry you from point A to point B.
But for now, your bags will remain the only thing that gets weighed at the airport.