laugh your head off
laugh (one's) head off
To laugh uproariously or hysterically. Your jokes are perfect for your speech tonight. You'll have them laughing their heads off! I'm telling you, Mark's boyfriend is hilarious! He had me laughing my head off when I met him.
laugh one's head off
Fig. to laugh very hard and loudly, as if one's head might come off. (See also cough one's head off. Fixed order.) The movie was so funny I almost laughed my head off. I laughed my head off at Mary's joke.