Related Clues:

• One might start 'Knock knock ...'
• One-liner, for instance
• Lost his head, during the summer before, with funny reaction
• Comic's currency
• Cause of the giggles
• React to a joke
• Amusing remark
• Ridiculously inadequate sort
• Ha-ha elicitor
• Fallon monologue bit
• Orator's icebreaker
• Response from the tickled
• React with mirth
• *Bit of blue humor
• Sitcom track sound