Disdain is worse than useless. It's toxic, erosive, mean-spirited and counterproductive.

People are people, and no less so (and no less adult) for doing whatever honest work it is that puts food on the table. It's been my observation over the years that many people are rude (especially to people in service jobs) because:
A) it's a place where they feel free to vent misdirected anger because they can get away with it, knowing the target "has" to put up with it and
B) think it makes them look superior.

It doesn't.

It's true what they say about the wisdom of observing how a suitor treats a server in a restaurant...

Hey, xxxispillcoffeexxxx! I spill coffee too!
I can only think of a couple of other ideas to add at the moment. One thing with social anxiety is a discomfort with the immediacy of conversation, yes? (As opposed to, say, email, where you get more time to think what you'd like to say.) If that is the case for you, try to note how many times "stock" lines can be fallen back upon. Realizing that the wheel doesn't need to be invented anew in every encounter can go a long way in taking the pressure off. The second one I've found not only helpful, but amusing(!) Switch your brain to therapist mode. Nope, no need to counsel, just detach yourself to a point of being an observer of human behavior. It helps in making it feel less like personal attack. The majority of the time it is their problem. They're just projecting onto others. I can remember one boss in particular who had a special knack for projecting like a mofo and making everyone feel like crap and frankly, as if they were incompetent (though they were far from). Guess who made the most errors? By a mile. Yeah. Being able to step back to a more objective place was a huge help in not taking the unwarranted comments to heart. (Some unpleasant criticisms are warranted. Own those, make the error right if you can, then move on.) Not willing to fall victim to his behavior, I simply detached to being able to see him as an "interesting case study". I didn't need to feel intimidated, or butt heads or hate him. I was too busy watching psychology in 3-D technicolor action. Does this mean I ceased to see him as a person? Not at all. It actually helped me through the worst behavior, to keep my head clearer for other interactions instead of being lost in obsessing or feeling wounded.

Oh, wait! There is one more. When you punch out at the end of the day, take a deep breath and leave it there. That tends to be one of the perks of hourly work. You don't have to take it home with you.