knock someone down with a feather

Meanings:

• 1.

  UKUSAustraliaCanadainformalidiomatic
  • To astonish or surprise someone so greatly that they appear stunned or incapable of reaction.
  • To describe an event or fact as extremely unexpected or remarkable.

• 2.

  UKUSAustraliaCanadainformalidiomaticcolloquial
  • Used in negative constructions to indicate that something is not surprising at all (e.g., could not be surprised even by an extremely light blow).