Preheat oven to 200 degrees F. Line 2 baking sheets with foil.
In a large bowl, beat egg whites with an electric mixer until frothy. Add vinegar; beat until soft peaks form. Increase speed to high and gradually add sugar; beat until glossy stiff peaks form. Beat in vanilla.
Remove half of meringue to another bowl; stir in cocoa until blended. Spoon tablespoons of both meringues onto prepared baking sheets about 1 inch apart. Each making about 44 cookies - half vanilla flavored and half cocoa flavored. Or bake until meringues feel dry and crisp all the way through, about 3 hours. Turn off oven; leave meringues in oven for 1 hour. Transfer baking sheets to wire ranks to cool completely. Peel meringues off foil and store in an airtight container at room temperature.