"I'm a Loner" (외톨이야; Oetoriya) is a song by South Korean pop-rock idol band CNBLUE. It is the debut and lead single to the band's first mini-album Bluetory. Written by Han Seong-ho and Amen, the punk-rock track was released under FNC Music on January 14, 2010. Upon its release, CNBLUE achieved immediate commercial success; the song earned the band its first two music show wins on Korean Broadcasting System's (KBS) Music Bank and Seoul Broadcasting System's (SBS) Inkigayo. Unprecedented at the time, CNBLUE held the record for shortest period between debuting and earning a music show win for four and a half years. The song also peaked at number two on the Gaon Digital Chart.

The composers Kim Do-hoon and Lee Sang-ho faced a lawsuit filed by indie rock band Ynot? two months after the release of "I'm a Loner". The band accused the two of plagiarizing one of its songs; a judge would later dismiss the charges.

"I'm a Loner" is classified as a punk-rock track. The song was written by Han Seong-ho and Amen, and composed and arranged by Kim Do-hoon and Lee Sang-ho; it is composed in the key of D minor using common time with a tempo of 105 beats per minute. Writing for Newsen, reporter Cha Yeon described the track as a "modern punk-rock song" with an "addictive" and "strong" melody. She noted that the guitar riffs and chord progression produced a "refined charm", which offered an alternative to the hook songs of other idol groups at the time.

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