This is a joint single between rapper Machine Gun Kelly and Camila Cabello, who was still a member of Fifth Harmony at the time. The song is about a sexually charged relationship between a good girl and a guy from the wrong side of the tracks. Cabello sings about her feelings for her bad boy lover while MGK tells her about the dark but pleasurable things he will do to her.

Cabello commented to Genius: "I think it's beautiful and I felt connected to it right away - the beauty and contradiction of innocence of the 'good' girl character who has these feelings about the 'bad' boy that she just can't deny.

Cabello interpolates Fastball's 1998 hit, "Out Of My Head" during the chorus, bending that song's meaning to fit the sexually charged narrative of "Bad Things." Asked by Billboard magazine if he was bothered by the flipping of his original words, Fastball singer-songwriter Tony Scalzo replied:

"Not at all. I think it's great, because it's super-creative… it's something totally different. I'm not totally familiar with the artists - obviously I did a little research a month ago when it was brought on the table - but I think that they basically were familiar with the tune, right? I don't think they went as far as to even try to cover the tune, they just basically re-wrote a lot of the words, and changed the meaning around, and that's really innovative and awesome."

MGK told Billboard magazine that when he started working with the song's producers, The Futuristics, he was excited to hear their interpolation of Fastball's hit. "We went through and we started to add more, 'Let's put two guitars on it, let's add some strings,'" he explained. "And when we were listening I thought, 'Man, everything else on my album and everything I've been doing lately has a very authentic feel... so I wanted to put that realness to it."

MGK recruited Cabello after being blown away by a YouTube clip of her singing with just some guitar accompaniment. "She was belting the notes out, not using Auto-Tune, and it was just beautiful," he recalled.

The collaboration was long-distance and the pair would constantly FaceTime to discuss the direction, with Cabello doing nearly 100 takes to get her vocal just as MGK wanted.

The song was the debut Top 10 Hot 100 hit for both artists. Asked by Billboard magazine why she thought the song caught the imagination of the public, Cabello replied:

"I think everybody can relate to going crazy for someone and, even if it's just in your mind, somebody bringing out a wild side in you. Also, with this duet there are two different points of view: A point of view of innocence and a point of view of someone wild, and everybody out there can relate to one."