When you want to get Fruitopia, but you accidentally press Nestea on the vending machine. Can apply to many different things, such as making a right when you were thinking of making a left, or circling answer B) when you were thinking of answer C.
Person A: Be right back, going to get a Fruitopia
*2 minutes later*
Person B: I thought you wanted a Fruitopia, that's a Nestea.
Person A: I was thinking Fruitopia but pressed Nestea. It's the Nestea Effect.