When we are "mad about something," we are usually expressing a strong emotion of anger or frustration towards that thing. Some synonyms for this phrase include "livid," "furious," "enraged," and "incensed." These words all convey a sense of extreme anger and are often used to describe someone who is out of control or losing their temper. Other milder synonyms for "mad about something" might include "irritated," "annoyed," or "peeved." These words express a less intense feeling of anger, but still convey a sense of dissatisfaction or discontentment. Ultimately, the specific synonym you use will depend on the level of anger you want to convey and the context in which you are speaking.