"Must you?" is a phrase often used to express annoyance or frustration with someone's behavior or actions. Instead of using this phrase, there are several synonyms that can be used to convey the same message in a more polite manner. For instance, you can say "Is it necessary for you to..." or "Would you mind..." as an alternative to "Must you?". Moreover, you can use "Do you have to..." or "Could you refrain from..." to express your disapproval. It's essential to use these phrases with a courteous tone to prevent sounding rude or disrespectful. Overall, using these synonyms can help you communicate effectively without being impolite.