In Catholic teaching, mortal sin is a grave¹ rebellion against the Laws of God made with full knowledge and consent, and which cuts the soul off from sanctifying grace.
The official Catholic teaching is that unforgiven mortal sins condemn a person to hell but lay Catholics debate whether this really is true or not.²
The Catholic Church also teaches that biological, psychological and social factors can lessen the seriousness of otherwise mortal sins if full knowledge and consent are not present.
TV shows, movies and video games tend to glamorize violence and killing. But for Catholics – clean ones anyhow – there’s nothing cool about eternal suffering in the next life.
Our world is so corrupt and lost in the dark, however, that many people have it upside down—hence the pop culture phrase “I’ll see you in hell.”
Not to suggest that people would go to hell for simply liking a Hollywood phrase. And I am not against the artistic representation of evil and sin. But I do think the whole notion can become somewhat misguided when creators cross the line between artistic representation, on the one hand, and crass glorification and exploitation on the other hand.
But that’s just my take. Where that line is – or if it exists at all – is open to debate and seems to be changing at an ever-quickening pace.
¹ See, for instance http://forums.catholic.com/showthread.php?t=493159