"RBB (Really Bad Boy)" is a song recorded by South Korean girl group Red Velvet for their fifth Korean (eighth overall) extended play RBB (2018). Written by SM Entertainment songwriter Kenzie and Sara Forsberg with production by Timothy 'Bos' Bullock and MZMC, "RBB (Really Bad Boy)" is primarily an "addictive" R&B and dance-pop song with influence from jazz and hip hop, with the lyrics expressing the charm of a "bad boy".[6][7] It was released as the lead single from its eponymous extended play on November 30, 2018, by SM Entertainment and Iriver Inc as the distributor, along with an accompanying horror-themed music video. Upon its release, "RBB" received mixed to positive reviews from music critics who deemed it "controversial" and "unfamiliar" to the public. The song however, gained compliments for its "unapologetic" boldness thanks to the group's experimental path. Domestically, it achieved moderate success in its native country, becoming their eleventh top-ten entry on Gaon Digital Chart, while being a bigger success outside of their native country, peaking at number one on Billboard's World Digital Song Sales. Background and release Three months after the release of their second summer special release Summer Magic, SM Entertainment confirmed that Red Velvet would return in November with a new extended play, titled "RBB" on November 30, 2018, and its eponymous lead single title. During a V Live broadcast, member Yeri stated that the preparation for the album was longer than their other releases, while member Seulgi noted that the song would be "very different". Following a music video teaser uploaded one day prior, the song's music video was released on November 30, 2018, to coincide with the parental extended play's digital release. Composition "RBB (Really Bad Boy)" was composed and produced by SM Entertainment songwriter Kenzie, producer Timothy 'Bos' Bullock, singer-songwriter Sara Forsberg (known professionally as SAARA) and MZMC. In an interview with Balloon Days, Bullock revealed that "RBB" was the last song to be composed during his 2-week writing camp at Seoul, South Korea, without knowing "who the songs were going to end up going to". The demo version was originally guided by Bullock himself and co-composer Forsberg, with additional Korean lyrics written by Kenzie after. Originally recorded in Korean, an additional English version was also recorded and included as the sixth track of the extended play, marking the group's second song to be recorded in English following their earlier release "Bad