I live in China, where we have lots of Hui Muslims. The level of devoutness among this group of Muslims varies considerably, with many who are not all that up tight about following (or are even aware of) the prohibition on alcohol (see: Qur'an 2:219; 4:43; 5:90）. F. Yang and J. B. Tamney, Confucianism and Spiritual Traditions in Modern China and Beyond, 2012, p. 208, writes:
One of the most significant customs of the Chinese Muslims, including the Hui and other groups, is the taboo against eating pork. In the Koran, drinking alcohol is consdered a more serious sin than eating pork, yet many Chinese Muslims drink alcohol while remaining very sensitive about pork.
Thus, it's possible I might end up in a situation in which a Muslim friend drinks alcohol in my presence.
Question: If a Muslim friend started drinking alcohol in front of me, how can I appropriately react?
I wouldn't know how to react appropriately in this situation.
I could condemn their actions, but this seems like an overreaction as it's not my decision to make. And it's hardly like I condemn non-Muslims for drinking alcohol.
I could ignore it totally, but this seems improper also.