From Season 1, Episode 4, Return of the Shirt (2005), Ted refers to the Belle & Sebastian song that Natalie always listened to, "We Rule The School".
It's from the scene where he remembers how he broke up with Natalie.
The episode was about Natalie whom Ted dated back three years ago and quickly got annoyed by some of her antics. Therefore he broke up with her, leaving a message on her answering machine on her birthday. His blamed his behavior on his immaturity and after being forgiven by Natalie they end up getting back together.
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