Season 1, Episode 7: "A Movie Script Ending" by Death Cab for Cutie
Death Cab for Cutie was Seth Cohen's first true love in the show (sorry Summer), so there are many Death Cab songs played throughout the series. The scene best known for showing Seth's unwavering dedication to the band was in season one when Summer throws serious shade and Seth passionately defends his beloved with the line "Don't insult Death Cab!".