The phrase "laughs one head off" means to laugh uncontrollably or to burst out laughing. Some synonyms for this phrase include cracking up, bursting out, doubling over, guffawing, and cackling. Other phrases that convey the same meaning include laughing till you cry, rolling on the floor laughing, and chuckling uncontrollably. These phrases are often used to describe something that is incredibly funny or amusing, and they are commonly used in casual conversations, stand-up comedy performances, and social media posts. Whatever the context, laughing one head off is a great way to relieve stress and express joy and happiness.