My point was that you would not make a similar 'tongue in cheek' comment about black people, or Jewish people, etc etc.
Bigotry against fat people for some reason seems to be a lot more acceptable than bigotry towards other groups is these days.
I don't think bigotry in any form is acceptable.
I do agree with your point on people needing to fit into their seat, otherwise they should buy another seat, but making bigoted remarks about fat people - who you can't tell by looking at them whether they are just eating too much or whether they have serious medical issues - is just as unacceptable as making bigoted remarks about any other group of people.