"As mad as a March hare" is a common phrase used to describe someone who has lost all their sanity and is uncontrollably crazy. There are several synonyms for this phrase, including "as crazy as a loon," "as wild as a buck," "as nutty as a fruitcake," and "as daft as a brush." These expressions are commonly used to portray a person who is out of their mind, with their behavior bordering on lunacy. Regardless of which phrase is used, the meaning conveyed is the same. It paints a picture of someone who has lost their grip on reality and is acting in an irrational, unpredictable, and sometimes even dangerous way.