“Bad Girls” was the leading single of the album: Monochrome is the fifth studio album by South Korean singer-songwriter Lee Hyori. It was released on May 21, 2013, by B2M Entertainment and distributed by CJ E&M Music. Unlike her previous work, Lee collaborated with foreign composers such as Norwegian songwriting team Dsign Music, who previously composed Girls’ Generation’s “Tell Me Your Wish (Genie)” and “I Got a Boy”. The album’s lead single “Bad Girls” is a dance tune only consisted of acoustic band sound. Lee’s self-written lyrics depicts the reality, in which confident women are considered “bad”. CJ E&M Music, the distributor of the album, released a video teaser for the track on May 15, 2013. As a parody of SBS’s current affair program The Its Know, the teaser stimulates curiosity through narrations such as “Why did Lee Hyori become a bad girl?” and “From now on, we’re going to unleash the truth about her”. Lee spoofs Sharon Stone’s interrogation scene from the 1992 film Basic Instinct. According to the singer’s agency, two versions of the music video, a story-centered one and a choreography-centered one, would be released. The former features cameo appearances from designer Yoni P, Gil of Leessang, model Jang Yoon-ju, SPICA member Ju-hyun, and actress Kim Seul-gi. The latter was released on May 23, 2013. “Bad Girls” went straight to number one on both the Gaon Singles and Download Charts in the first week of June 2013, as the album’s pre-release single did. It also topped the Billboard Korea K-Pop Hot 100 for the week of June 8, 2013, becoming her first song to reach the chart’s pole position, a week after debuting at number 25. This song won the first place on televised K-pop music shows like SBS’s The Music Trend, KBS’s Music Bank, MBC Music’s Show Champion, and Mnet’s M! Countdown, from June 2 to 13. As of May 2021, “Bad Girls” has sold about 900,000 digital copies in South Korea. Lee performed “Bad Girls” as part of a highly praised collaboration stage at the 2013 SBS Gayo Daejeon televised concert, along with CL from girl group 2NE1, who had also released a bad girl themed song that year called “The Baddest Female”.