I've often had friends tell me there is something wrong with me, when it comes to that aspect of gaming.
Most often, I play evil first - as it allows more exploitation of the environment without unwanted effects.
If the game was good, I go back and play good.
Then, and it doesn't happen often, a game allows me to "unleash the beast".
Prime example:
Black and White (The first one).
Right off the start there is a "quest" or objective.
You need to obtain three totem-pole-stone-thingies.
One of these stones are inside a village-woman's house.
Her brother is missing. He is also deathly ill. If you find him and bring him back to her, she will give you the stone.
The good way is to go fetch the brother and re-unite the two.
The bad way is to smash the house open and take the stone.
My way?
Break the house. Take the stone. Kill woman with stone.
Pick up dead woman and find ill brother. He is on a cliff by some trees.
Drop dead woman in front of him.
"Oh! My sister! I can't continue living!" - jumps off cliff...
...continue to snicker and go put stone on totempole.
I love when a game unleashes some creativity into the whole dark side. Simply killing everything for no reason gets stale, unless you can do it creatively!