Preheat oven to 350 F and line pans with cupcake liners.
Sift cake mix and cinnamon into small bowl; set aside.
In large bowl, combine eggs, melted butter, buttermilk, sour cream, and vanilla extract.
Add cake mix and stir until smooth.
Fill cupcake liners ¾ full and bake for 17-22 minutes or until knife inserted near center comes out clean.
For buttercream; beat butter and cream cheese for 2 minutes.
Add vanilla extract.
Slowly add powdered sugar until buttercream reaches desired consistency.
If it becomes too thick, add milk.
Pipe buttercream onto cooled cupcakes and top with stylish mustache.
If using paper mustaches, wait until just before serving to place on cupcakes.