I also just have to throw this Cracked article out there.
We can only judge other beings from our mindset. We can't really say anything about other creatures, except that they are not as intelligent and technologically advanced in human sense. Animals, fish, insects might have social and cultural level that we are just not capable to understand and measure with tools and knowledge at our disposal. Something, that looks evil for us might be absolutely normal and even pleasant for them. There is a movie - Unthinkable. It shows what humans can do, how evil their actions might be. But then you see that even the one who objected against all of this takes part in it. Now imagine thousands of years of acts like this. What if mantis females, when eating male's head after mating, do so to prevent death of their children? Can this still be considered evil?...
On topic, I think the most disturbing and evil things I've done in video games was burning Bob with a Flamer in Fallout 3.
Morals are not instincts.
They are really roles of conduct we have formed over thousands of years, it still varies from culture to culture.
Some things can be described as instinct. Like not killing members of your 'group', as that would also lower your own chance of survival. (usually)
The most evil thing I've done is child abuse.
Although, when a kid runs up to you and asks you to turn them invisible and you have a lightning rune in one hand, you try to resist the same temptation I had.
"Wow, are you doing magic? Can you turn me invisible?"
"Sure thing kid." BAM!
Kid knocked out, Nazeem dead on one side, half the health of a guard gone on the other. Total: 1120 bounty.
I don't mean to spark a debate, but I think someone should put forward the Christian view of morality. God created mankind and gave us the knowledge of good and evil. That is what differentiates us from animals. So no, animals don't have a sense of morality. That doesn't necessarily mean that they don't feel some primitive emotions such as affection or anger.
There is an easy way not to spark a debate. If non-Christians practiced the tolerance they advocate, then you would just let me state my view and move on. I'm happy to debate if anyone wants to, but don't tell me that stating my view is forcing people to adopt it. I'm doing only what everyone else has done who has posted in this topic.