Ok, I'll admit to a bit of MULE... although, we didn't have a fancy acronymn for it. I was working SFO/OAK/SJC arrivals / departures to the southeast (Area A @ ZOA) at the time.

The issues then (1989-1998) were that, of course, SFO is a UAL hub. So there were a lot of UAL flights. At the time, the "fancy" new FMS equipped B757's were entering service, and these guys were clearly not used to the equipment. And, they weren't overly prepared for the new, slick plane that gathered speed in the descent. Many complaints of "we can't go down / slow down in this plane".

Plus, they tended to just complain a lot in general.

Then, a new kid entered service into SFO / OAK. Southwest replaced the "Can Do Easy" attitude of PSA. They always made it work. I never got a pizza, but I never had an issue with a SWA crew.

In one instance were a UAL crew actually called the facility to complain about me allowing SWA to leave the holding stack in front of them. They were accurate, I did do that. But, because SWA was actually in a position to exit holding and move on. I have no idea what this UAL crew was doing. I would say that actually calling my work to "turn me in" probably didn't help the UAL cause for me. I considered calling UAL ops in SFO every time one of these guys screwed up. Never did though.

I went to SoCal Approach in the spring of 1998, so my ATC contact with UAL after that was minimal.