“Casual Affair” details the secrecy and thrill of having a one-night casual affair. The song buzzes with high energy synths along with plenty of low end rhythm.

Urie discusses the allure of a casual sexual encounter in an interview with RockSound:

Even when you’re with somebody, your mind still wanders. There’s always the fantasy. Me and my wife always talk about our celebrity crushes […] That’s where this song came from: living out the fantasy in your mind without actually going through with it.

Interestingly, the intro to the Youtube version of the song is taken from the 1961 anti-gay propaganda film “Boys Beware”.