be laughing your head off
be laughing (one's) head off
To be laughing uproariously or hysterically. Your jokes are perfect for your speech tonight. They'll be laughing their heads off! I'm telling you, Mark's boyfriend is hilarious! I was laughing my head off when I met him.
be laughing your head offINFORMAL
COMMON If you are laughing your head off, you are laughing a lot. They were probably laughing their heads off. Note: You can use other verbs with similar meanings to laugh in this way. Laura was sitting inside, giggling her head off.