Flufferkncukle is a made-up word from the kids book, "Pottymouth And Stoopid". Pottymouth made the word and he uses it as a replacement for the "f-word".
When you fail at something in life (eg. failing an exam or not getting a job), go home and spend an hour just standing in the shower, propping yourself up against the wall with your eyes on your feet.
Caleb knew the only thing to do after he didnt get prefect was take a failure shower.