A hip hop-influenced R&B number, its lyrics were written by JQ and Moon Hee-yeon whilst music was handled by the Stereotypes, Maxx Song, Whitney Phillips and Yoo Young-jin.

Their appearance at the concert made them only the fifth idol group to ever perform in North Korea and the first artist from SM in fifteen years since Shinhwa.

[6] Since January 26, teaser images of all members were eventually revealed through the group's social media platforms, with journalist Kang Seo-jung of Osen commented had the vibe of a powerful "eonni".

The song then returns to its chorus section for the last time, including additional sounds such as walking in heels, riding motors and cars' siren before ending.

[12] Mexican news site Milenio called the song's melody a mix of R&B and hip hop and stated that its lyrics tell the story of the beginning of the couple's relationship.

[16] Fuse's Jeff Benjamin felt that the group put their own spin on modern R&B and hip hop and compared it to other artists such as Rihanna, Tinashe, and Cardi B who have incorporated "sassy, catch phrases into their verses and choruses".

Writing in the article, L. Singh called "Bad Boy" the "perfect representation of their mature 'velvet' persona", and further praised its composition, commenting on "how tactile the sonic and visual layering of the song is".

[36] In April 2020, "Bad Boy" was certified Platinum by the Korea Music Content Association (KMCA) for selling over 2,500,000 downloads, marking Red Velvet's third song to reach the milestone, following "Red Flavor" and "Russian Roulette", but the group's first to receive a KMCA certificate following the introduction of certificate system in 2018.

[39] Furthermore, "Bad Boy" was the group's first entry on the Canadian Hot 100, entering at number eighty-seven for one week, thus becoming the third female act, and subsequently the seventh overall K-pop artist to appear on the chart.

An accompanying music video directed by Kim Ja-kyoung of Flexible Pictures and choreographed by Japanese hip hop dancer and choreographer Rie Hata, who had previously worked with CL for the choreography of "The Baddest Female" and with the group's label mate BoA for her single "Nega Dola", was released on the same day as the album and song.

[41] The video was called 'sultry' by Annie Martin of UPI and it featured the members in various coordinating outfits, which included all-black ensembles and pink pajamas.

Talking about the choreography, she said that it was "filled with suggestive hip rolls and aggressive come-hither hand motions, beckoning sultrily toward the audience and shooting at the camera".