28 “Let my slanderers be clothed with shame”: that is, let it shame them to have slandered me. But this may also be understood as a blessing, in that they are amended. “And let them cover themselves with their own confusion, as with a double cloak;” for diplois is a double cloak; that is, let them be confounded both within and without: both before God and before men.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)