I forgot to mention that, when I phoned the CVS store to find out the name of the store manager (so that I could cc him on the letter), the manager practically begged me — repeatedly — to let him handle it, rather than writing a letter to the corporate office. Three separate times, he pleaded with me to wait and see if he could "resolve the situation to [my] satisfaction" before "taking it to the next level." I told him that I really doubted that he could do anything to rectify this particular person's attitude or behavior, and so I would rather just write the letter.
His frantic efforts to get me to keep mum made me think that sending a letter to the corporate office might actually have some effect, even if it is only to get the manager in trouble for hiring that particular pharmacist.
I generally think of such letters as simply a way of getting something off my chest & don't expect that they will have any real impact in corporate America, but it would be nice if this store manager's fear was justified & my letter actually has the power to make something happen.