Place 1/4 cup whipping cream in a medium bowl. Beat with a mixer at high speed until stiff peaks form.
Heat 6 mugs by running under very hot water; dry with paper towels.
Pour about 4 teaspoons whiskey into each glass. Add 2 teaspoons sugar
to each serving; add 2/3 cup coffee, stirring until sugar dissolves.
Top each serving with about 1 1/2 tablespoons whipped cream (do not