The Fairly OddParents (2001)

S3E13 The Secret Origin of Denzel Crocker

March 15 strikes fear into the hearts of every child, as it's the day when Mr. Crocker is at his most vicious, and no one knows why he’s so miserable. Determined to uncover the truth, Timmy hops on the Time Scooter and travels back to Crocker's youth. There, he discovers an astonishing secret that links Crocker with fairies in a surprising way.