[peteram]

FWIW: On the video clip on TV, the man sueing the airline demonstrated how the obese passenger lifted the armrest between them so there would be no obstruction to him sitting. This resulted in the skinnier passenger losing a third of the seat that HE paid for and having to be pushed against the opposing armrest for the duration of the flight.

If this was indeed the case, then - yes, he should sue.

[Gunrunner2]

When you buy a ticket from an airline you are entering into a contract. That contract says that in exchange for a few dollars, when your purchase a single ticket the airline will sell you a single seat (no more, no less, a full seat).

That said, when a fat passenger spills over and takes more than one seat, that passenger is violating his terms of the contract (taking more than he purchased). In addition, the airlines are violating their terms of the contract if they could reasonable tell the fat passenger would use more than one seat and refuse to insist the fat passenger buy more than one seat--basically to pay for what he uses.

So, in this situation you have one injured party and two violators.

Sue the fat person and the airlines, or maybe even file criminal charges against the fat passenger for Theft of Services.

In any case, the inncoent passenger should not be deprived of his contracted and paid for service and accommodation.