Killing NPCs has always been a macabre past-time in every open-world game, especially the Grand Theft Auto games. Slaughtering random characters in video games is nothing new; almost every game does it in some form, but its the open-world games that allow for a kind of morbid creativity to foster. The most ambitious of these, Grand Theft Auto V, has pushed this past-time into high gear, with players adopting a newfound interest in showing their creativity with bloody NPC kill videos.
In this day and age it's very easy to broadcast and post your in-game feeds, so it's no surprise that GTA V gamers are posting up tons of their favorite "kill cam" or "most brutal kill" videos. These videos are popular, pushing the past-time into a new evolution, and tons of gamers are competing with one another to find new inventive ways to kill NPCs. A portion of these videos are extremely popular, ranking in the tens of millions of views, showing just how alive and well this fascination with torturing in-game characters actually is.
Most of the time, players find killing NPCs to be humorous. Sometimes it's about pushing the limits of the in-game world to see what you can do, and who you can do it to. I think we've all done things like this, and I think this kind of thing happens when there's a big lull in any kind of singleplayer DLC for open-world games like GTA V: but even with all the DLC in the world, people would still occupy themselves with this past-time, playing a kind of virtual god in their own sphere of influence.