Damon has no trouble wiping out almost an entire family as part of his revenge plot.

Remember how Damon wiped out almost an entire family? That's because he left a single orphan alive so he could repeat the cycle with the next generation.

Damon has no problem taking Enzo's blood rations to ensure his own strength to escape. The deal is that he'll return to release Enzo, but it's surprisingly easy for this psychopath to protect only his own back.

Damon offers Elena one face and his victims another. Duplicity is no problem.

Again, Elena gets the pretty face that will ensure her loyalty so Damon gets what he wants from her.

These psychopaths enjoy a healthy dose of self-adoration.

Torture, murder, suppressing one's humanity -- all minor incidents one can let go of once they're in the past, right?

Klaus can easily blame his whole family for how they treated him, but he will never see fault in himself.

Klaus is unmoved by his sister's tearful declarations of loyalty. Love and compassion are foreign to him.

Not only are psychopaths incapable of feeling emotions, they can't even understand them in others. To Klaus, Rebekah's grief is totally incomprehensible.

Like the real-life serial killer Jeffrey Dahmer, who tried to create compliant zombies, Klaus is only interested in people who will comply wholly with his will.

Psychopaths often know how to put on the right airs to get what they want, like when Klaus tried to get to know Caroline better.

In both Damon and Klaus, we see the irresistible desire to be in control, even at the cost of someone else's free will.

To a psychopath, a person's value lies entirely in their usefulness to that individual. Damon sums it up well when he refers to humans are toys, tools or food.

When life is a game, why not frame Lexi for murder and stake her for it in front of the sheriff? Now that makes for good TV.