I know that Season 4 isn't generally considered the worst, but Best Day Ever was the conclusive point when the series lost its classic zany Nicktoons vibe and became a generic vehicle to sell backpacks and CDs at Walmart. The marketing around this episode was massive, unbearably annoying, and totally embarrassing. Even as a kid, I remember thinking "OK, that's enough of this show" when I first heard the fucking song.