if you do something for the hell of it, you do it only because you want to, or because you think it is funny I decided to dye my hair bright green, just for the hell of it.
Also, for the heck of it; just for the hell of it. For no particular reason; on a whim. For example, We drove by the old place just for the hell of it. In the first variant, heck is a euphemism for hell. [First half of 1900s] Also see for fun, def. 2.