Lyrically, “Mr. Brightside” depicts the jealousy and paranoia of a man who suspects his significant other is cheating on him. Guitarist Dave Keuning composed the music before meeting Flowers. Flowers then wrote lyrics and composed the chorus after hearing Keuning’s ideas. Flowers credits the speed of the song’s creation due to it having only one verse. He says, “We went in and made demos pretty quickly after that, and it took a ton of time. That’s also why there’s not a second verse. . . I just didn’t have any other lines and it ended up sticking. ” Drummer Ronnie Vannucci Jr. is credited with creating the fast-paced drum beat in the first twenty-two seconds. The “calling a cab” section of the song has both a musical and textual similarity to the middle section of the song “Queen Bitch” from David Bowie’s album Hunky Dory (1971). “Mr. Brightside” is written in the key of D♭ major.