My dirty secret is that I really like the player characters and do not want them to die. I keep the illusion going that I like to kill PC's as if It gives me DM Creed with my fellow DM's. I run the game as slightly antagonistic while in reality I am a pushover and love to see the pc's beat the crap out of my favorite npc's and villains.
I really love it when they are in a (unbeatable) situation and then they think outside the box and find that one thing the godlike genius 5,000 year old lich didn't think of and trash him. I like to look stricken and flip through my notes in frustration (like I really have pages and pages of things the lich did think of)and disgust and then weakly try and negate the idea with a weak reason why it wouldn't work and see that gleam in their eyes and let them provide work arounds and reasons why I am wrong.