There are some things you can't get out your head. Things like the way a girl you have a crush on walks, road kill on the side of the road, the electric feeling of an oncoming performance, the taste of your favorite food, or the moments when you first fell in love.
In their case, it just would not go away. They wanted the memory of her to be washed away, like it never happened. Like she never existed. Because she doesn't anymore.
Santana wanted to pour bleach in her brain, to fry every memory out of her head. She wanted to be anyone, anywhere, anytime else. She just didn't want to be.
Finn wanted to pretend, act like she was just a made-up character he used to dream up when he was younger. That the sound of her voice was just nothing he'd ever had really heard. Her face was just something that was stuck in his mind. Her watery-blue eyes a color that wasn't possible.
If it was up to them, Brittany Pierce had never really existed at all.