In a word: Deal.
The workplace is not there for your comfort. Bosses are mean, customers are mean, coworkers are mean. Get a thick skin now, or you never will.
I just started my job on campus at a call center 2 days ago. Not only was I horrible at getting donations, but I quickly felt uncomfortable with the job and what it was asking me to do.
Two days is hardly enough time to become proficient at anything. and unless they are asking you to do something illegal or unethical, your discomfort is irrelevant. A job is not designed to make you comfortable. that is why it is called work and not play.
Because of scheduling issues, my supervisor is usually unavailable to meet unless it's time for work, and I know he would patronize me in front of everyone there and I don't want to have to see him, but I don't want to discredit myself.
Quitting after only two days is in and of itself discrediting yourself. A dressing down from a supervisor over it is not. Actions have consequences.
How do I do this?
My recommendation is to stick it out for a while. Talk to your supervisor about any difficulties you are having and come up with a plan to overcome them. If the work turns out to be something that is not for you, be professional and give the standard two weeks notice, or, if you can, give notice with the understanding that you will stick it out until they can find a replacement.
Your supervisor will likely dress you down for giving up, but that is life. Learn from it and become a stronger person for it.