In this article, I reconsider the question of how best to understand Sartre's concept of bad faith by investigating it through the Derridean lens of deconstruction. I argue that Sartre's discussion of bad faith in Being and Nothingness mirrors Derrida's criticisms of structuralism in 'Structure, Sign, and Play in the Discourse of the Human Sciences'. Examining their distinctive discussions of 'play', I claim that Derrida's unique deconstructive interpretation of this notion operates within Sartre's criticisms of the 'spirit of seriousness'. I reinterpret bad faith as the attempt to solidify a permanent structure of one's personality, in order to avoid or escape from the 'play' or 'freedom' built into structures and our existential condition, and conclude that embracing 'play' is an essential characteristic of authenticity.