Is it normal to think about killing/torturing the people around you?

I sometimes fantasize about what it would be like to kill or torture people. Usually, it happens when someone irritates me to the point where I want to slam their head into the nearest wall until their skull resembles a blood-covered jigsaw puzzle. That's more or less normal, I think—we all want to kill somebody sometimes.

The bit I'm wondering about is if it's normal to get excited by it, or even get off on it. Just thinking about cracking the back of someone's head open on the curb or watching as they struggle for breath as I crush their windpipe with my bare hands makes my stomach churn in a pleasant sort of way.