"Bad Guy" is a song by the American singer-songwriter Billie Eilish and the fifth single from her first studio album, When We All Fall Asleep, Where Do We Go? (2019). It was released on March 29, 2019, by Darkroom and Interscope Records. The song was described by media as electropop, dance-pop, and trap-pop with minimalist instrumentation. In the lyrics, Eilish taunts someone for being tough while suggesting that she is a more resilient bad guy than he is. Eilish wrote "Bad Guy" with her brother and the producer Finneas O'Connell. Another version of the song, a collaboration with the Canadian singer Justin Bieber, was released on July 11, 2019.

Billie Eilish Pirate Baird O'Connell is an American singer and songwriter. She first gained public attention in 2015 with her debut single "Ocean Eyes", written and produced by her brother Finneas O'Connell, with whom she collaborates on music and live shows. In 2017, she released her debut extended play (EP), Don't Smile at Me. Commercially successful, it reached the top 15 of record charts in numerous countries, including the US, UK, Canada, and Australia.