Very intensely or loudly; with no restraint, hesitation, or inhibition. (Used after verbs associated with speech sounds, such as "yell," talk," "laugh," etc.) I'm telling you, Mark's boyfriend is hilarious! He had me laughing my head off when I met him. Suzy started yelling her head off when I told her she couldn't have an ice cream cone. A: "So, has Noah started saying any words yet?" B: "And then some—he's been talking his head off for months now!"