Do you like to kick or punch people in dreams? is one example, and there are plenty of other topics on this.

As I have said before, if we were all ideal people, I don't think people would be violent, consciously, or when dreaming. I think how we act subconsciously is a truer version of our waking selves. I believe such a sign of aggression in dream land is pointing out a flaw, a defect in us, and one should work to remedy it.

Usually I don't kill people though, if I do cause significant damage, they always keep getting back up. About the third time, I stop knocking the crap out of them. Here's one example when I was worse than I needed to be.

I was in a bowling alley, and noticed several female friends bowling. I picked up one of them, and took her to my dream apartment. I pulled off her underwear, to find a penis, instead of her clitoris. I was so mad at her for being a crossdresser, so I turned her over, gave her a tombstone piledriver, and broke her neck. Then I took her back to the bowling alley, and did it three more times right in front of her friends to add emphasis, as if to say "That's what happens when you cross dress, none of you other ladies better be like that".

I decided that if such a thing would happen again, I would simply suck on it and see what happens. Since then, it has not happened.