He was getting paid and everybody knows what they're getting into when they get a job in that industry. If you're not prepared to take shit from people, you shouldn't be in the fast food industry.
Let me make this quite clear... you represent everything that is wrong with the mindset of the fast food industry, and customer service industries in general.
There are NO circumstances in which it is acceptable to either verbally or, worse, physically, abuse someone who is just doing their job.
The customer service industry does a disgusting job of protecting it's staff from abuse by unreasonable individuals. The phrase "The Customer Is Always Right" has been discredited for the most part, but has left an indelible mark on these industries where people can get away with threatening and even performing violence for the tiniest of problems and not be dealt with.
Management in many of these companies are little more protected and able to deal with situations than the staff themselves. In fact, because the staff come from a wide variety of backgrounds, many of the staff are likely more capable. Both Staff and Management are paid pittance compared to other jobs, and expected to put up with the most atrocious abuse while knowing.. for certain.. that their company will not support them no matter what the situation.
Until you see the customer service industry doing what even, for example, my local rubbish tip, does for it's staff... protecting them from abuse and ensuring that anyone who is abusive is refunded and escorted from the premisses no matter what the situation, we will see incidences such as this.. where those of us who work in this industry know we have no choice but to protect ourselves and our own.