That's a tricky question.
I don't enjoy confrontation, and it's my instinct to be escape-focused when threatened with/experiencing violence. Aggression simply doesn't occur to me "in the moment". I am also particularly averse to the consequences of murdering someone in traditional societies.
That being said, I've never experienced a feeling of guilt or any kind of remorse for an action I've taken. Even my rare feelings of shame are deeply selfish. If I choose to do something, "wrong" or "right", I don't look back.
So, I can say with some confidence that in situations where external consequences for my actions are removed, and my own morality presents no obstacle, I could easily kill a person and sleep well that night.
Unfortunately, I can't think of a single instance where these conditions could exist. I hold myself to some fairly complex, if atypical, rules, and I doubt I'll be bestowed with a "license to kill" any time soon.