Chill a martini glass by filling it with 1/2 cup of ice and cold water.
Place 1 cup of ice cubes into a cocktail shaker. Pour the vanilla-flavored vodka, white creme de cacao, and Irish cream liqueur over the ice; cover and shake vigorously. Dump the ice and water from the martini glass and drizzle the inside of the glass with chocolate syrup. Strain the cocktail into the glass to serve.