I once found a small Garner Snake out in the back yard. As my brothers and I played with it for a time, we decided it would be a good idea to use it to scare my sister. So, into the house we went with snake in tow. Of course, I softly crept up to where my sister was sitting, with the snake hidden behind my back. As I got close enough, I quickly pulled the snake out from behind me and placed it close to her face. The resulting scream, I can still hear in my dreams. This was not the extent of my prank, though. She jumped up and I began to chase her. We made a round of the living room before she darted for the stairs, with me hard on her heels. She got into one of the bedrooms and locked he door, as I was ascending the stairs. So, I held the snake by the tail and let it wriggle under the door frame, to blood curdling screams. I have always felt bad about that incident, not for the initial scare but for the prolonged agony, with the snake under the door. That was definitely taking it too far and her tears really cut me deep. This was the last of my sustained attacks on my sister. Thankfully, she has forgiven me for my foolishness.
I think some people don't feel guilt because they have not truly learn to love. Some people's mind never develop much of a conscience. Whether this is due to bad parenting or simply an inherent disposition, the psychologists will have to determine.