I've heard the claim that psychopaths are constantly, or at least most of the time acting in order to manipulate people, most recently on an episode of Supernatural, episode 15 of season 7.
The dialogue was as follows:
Sam: So, Jeffrey was just pretending to be the victim.
Sam: Way back in that farmhouse during the exorcism, h-he was just...acting.
Dean: He was a psychopath, Sam.
Dean: That's what they do all the time, is act. Act like they're normal, act like they're not balls-to-the-wall crazy.
Another, perhaps more well known instance of this claim is the titular character on the TV shows Dexter, a self-proclaimed psychopath. It is mentioned throughout the show that Dexter has to act "normal" to fit in and avoid arousing suspicion. Quotes from Dexter demonstrate that:
Dexter: [voiceover] I like to pretend I'm alone. Completely alone. Maybe post-apocalypse or plague … whatever. No one left to act normal for. No need to hide who I really am. It would be … freeing.
Harry Morgan: But most normal people don't, and it's important that you seem normal. Teenage Dexter: Even though I'm not. Harry Morgan: Because you're not.
A major characteristic is that they don't feel empathy or remorse, so I take the claim as above to mean that they are acting to give the impression that they do.
Is there any validity to the claim that people diagnosed as psychopaths are acting a substantial amount of the time, significantly more than most people as implied?
I would guess any surveys or long-term observations could provide a starting point to answering this question.