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.
See also: head, laugh, off

be laughing your head off

INFORMAL
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.
See also: head, laugh, off
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