The phrase "be mad" is often used to refer to a variety of negative emotions, including anger, frustration, and irritation. There are a number of synonyms that can be used to convey similar emotions, including "be furious," "be enraged," "be incensed," "be vexed," "be irate," and "be infuriated." Other ways to express similar emotions include saying "be steamed," "be ticked off," or "be miffed." Regardless of the word chosen, it's clear that the person is feeling a great deal of negative emotion and is likely to be reacting in a strongly adverse manner.