How to you play evil? (Possible spoiler alert)

So, after many years and play-throughs of the game, I have finally decided to actually play through with an Evil party. In the past, whenever I have tried to do that, I always ended up giving up because of what was necessary (In my view) to maintain a low reputation. But I plan on pushing through this time.

On the whole, I don't like playing stupid evil. You know the kind of thing where, instead of sounding EVIL, you end up sounding like a spoiled and petulant teenager. But I realize that the more things you do in the game in performance of the plot line, the more you gain positive reputation points. Now, I realize that I could simply spike some commoner far away from the beaten path and thus reduce my rep. But without a real reason to do it, that just feels like meta-gaming your rep.

So I wanted to get ideas from the rest of you on what you do and what RP rationalization you use. If it helps, my Charname is a Half-Orc Fighter/thief. His main philosophy is basically being a Darwinist. What doesn't kill you makes you stronger. And if you are weak, you deserve to die. (Ok, I am sure that good old Chuck is rolling in his grave over that interpretation of his teachings, but hey...).