The phrase 'CRAZY as ___' is a popular idiom used to describe someone who is behaving in an irrational or unpredictable manner. The four crossword solutions for this phrase are LOON, ZANY, LOCO, and GAGA. LOON is a North American aquatic bird that is known for its wild and erratic behavior. ZANY is an adjective that means 'playfully eccentric or whimsical'. LOCO is a Spanish word that means 'CRAZY' or 'INSANE'. GAGA is an informal term that is used to describe someone who is behaving in an outrageous or silly manner.