Set aside 1 tablespoon chocolate wafer crumbs.
Beat whipping cream at medium speed of an electric mixer until foamy; gradually add sugar, beating until soft peaks form. Pour crème de menthe in a thin stream over whipped cream, beating constantly, until mixture is well blended.
Alternate layers of whipped cream mixture and chocolate wafer crumbs to fill 6 chilled parfait glasses, beginning and ending with whipped cream mixture. Sprinkle reserved crumbs over each parfait to garnish. Serve immediately.