People shake their nail polish to mix it evenly. Obviously. I do the same. But nothing annoys me more when people come into my house, grab my nail polish by the top of the lid and the bottom of the bottle and shake up and down vigorously. Why? It introduces more air into the polish, accelerating the thickening process. The other option to mix nail polish to quickly roll the bottle between your hands.
So lies my creed: Thou shalt roll, not shake, in order to mix.
Break my rule, I'll beat you to death with a spoon.