Hartington
If you look at the BA cabin crew dispute, where a large majority of lemmings voted to empower their union to strike for 12 days at Xmas and are now voting again, against a grim economic background and few, if any cabin crew jobs going elsewhere, the impression one gets is that many may not have a lot between the ears.
(Not all by any means, some BA cabin cew, such as Jetset Lady who posts here are very bright.)
However, if the majority are not over endowed with grey matter, then this might explain this 'term of endearment', since it is not overbright to use negative metaphors IMHO.
I always refer the clients in our business as 'clients', as that is the respectful term. They also pay the fees that fund my salary, a fact I never forget. They may be pains at time, but they paid for my house, my cars, my kids education etc.
My belief is that the names you call people do unconsciously influence one's feelings and behaviours towards them.
So Entaxei may have a point.
Having said that, I haven't experienced the dire airborne service that some report, in fact it is normally okay to good with BA; The ground 'experience' is my bete noir.