“Wake Me Up When September Ends” is the only song on American Idiot that has no direct connection to the album’s story arc.

Green Day lead singer Billie Joe Armstrong wrote this about his father, who died of oesophagal cancer on September 1st, 1982. The title allegedly comes from what 10-year-old Billie Joe Armstrong told his mother after his father’s funeral. He had locked himself in his room and when his mother knocked on the door, he replied, “Wake me up when September ends”.

This was originally supposed to be on Shenanigans, but Billie wasn’t emotionally ready to record it, so it was put onto American Idiot.^[[1] https://genius.com/Green-day-wake-me-up-when-september-ends-lyrics]