It is important to refrain from using derogatory terms such as "whiny little brat" when referring to someone. However, if you must describe someone's behavior in a more respectful manner, there are several synonyms you may use. "Complainer," "crybaby," "spoiled child," "entitled youngster," and "petulant individual" are all options that describe someone who frequently whines or complains. It is also important to consider the root of their behavior and address the underlying issues rather than solely resorting to name-calling or negative labels. By using more tactful language and addressing the root cause of someone's behavior, you can foster more positive and productive interactions.