Possible Clues:

• Absurd situation
• Cause of a laugh
• Kid (around)
• It's hard to tell if one's practical
• It has a punch line
• 'Is this some kind of twisted ___?'
• One might start with 'Knock knock'
• In French, I must grasp fine gag
• Crack all right in aeroplane losing tail
• A shaggy dog story is a long one