As a former controller of UK TC airspace I can only add my agreement to this topic.
Britannia Airways (Otherwise known as "Can we Airways" because of their incessant requests for direct/higher/lower etc etc) were the airline I disliked most while controlling.
There seemed to be a continual attitude that they were the only plane in the sky and we as ATC were a mere irritant to their progress through the clear blue skies.
I recall on one occasion I was working a heavy rush inbound at about 7:30 one morning, we had in excess of 20 minute delays at LHR, we were stack switching and my R/T frequency was saturated. All crews were demonstrating a high standard of R/T discipline and keeping readbacks to the minimum and we were just about winning. Until a Britannia outbound came along and after giving initial climb, he had to level off, at which point he began whinging for higher. After three calls from him I eventually and for the only time had to deliver a verbal tongue lashing because it was obvious the guy didn't have a clue about the situation going on around him. Not to mention his constant stepping on of other higher priority transmissions with "level at FLxxx, request higher".
It's not great to generalise in such a way but this was fairly typical of BY crews (not normally as bad as this), and I can tell you it does not endear yourselves to the coal face controllers who are actually there to keep you alive and try to help when possible, not to restrict climb/descent nor to deny direct to the centrefix for no good reason. Other airlines seem to play the game, BY at times not.
Again, let me be clear that I'm not tarnishing the whole airline, I have dealt with some fine BY crews, but instances of controller "harassment" do the rounds fairly quickly in the rest room and on the floor and anecdotal evidence and my experience is that BY is the worst offender by far.
Anyway having said this let me conclude by giving an example of the most unprofessional R/T transmission I ever heard............from an Airtours (At the time) crew.
I was listening in as a trainee and this AIH inbound had been bleating for descent all the way down looking for a straight in. The controller eventually had to level him at FL100 against outbound traffic at FL90. The pilot was whining and moaning and requesting lower at least three additional times, and when he was finally given descent his response was
"Well that's really useful now isn't it"
I nearly fell off my chair, unbelievable !