If the teller had made the disparaging comments only to you, you'd have no recourse other than 1) take your business elsewhere; or 2) complain to management and see if they choose to take action. Legally, though, a person may make any comments (s)he wants directly to another person.However, disparaging your business to third parties, especially your customers, could constitute defamation IF she made untrue factual statements--but if she only voiced her opinion, that is not defamation and not actionable (anyone may express any opinion; it's only untrue factual statements that may be actionable). If you think this is the case, you should discuss the matter in detail with an attorney, to see if it's worth taking action. Otherwise, you're left with complaining to management and/or taking your business elsewhere.