Expression used by a staunch minority, especially on Facebook, that indicates 1) an unstable and immature, or 2) a disillusioned and mature, perspective. Will always be perceived by others as the former (1), so it's probably best left excluded from your Facebook, or any other type of, profile.
"Ha, look: his Facebook relationship status says, 'It's complicated.' Boy is he a lost soul...and poor her."
"Yeah, maybe he's just cheating, or 'just' maybe he knows what's up about human behavior. Read up on it. Besides, not like you know what you're doing with your girlfriend either."
"Seriously folks, it's best to leave that part on your profile blank. It's none of anyone's business."