疯狂 (fēng kuáng) is the common two-character adjective for 'crazy, frenzied, wild' describing extreme behavior or emotions. It is broader than 疯 (fēng), which can literally mean 'insane' or is used more informally, and 狂 (kuáng), which often emphasizes 'unrestrained' or 'violent' behavior. Use 疯狂 as the general word for 'crazy' in everyday contexts.