Here's how I tend to operate:

If I kill someone and it's just a total beat down, then I get a chance to take whatever I want but take nothing, then that person drops to the bottom of my list. That is to say, I'm not going to actively hunt that person if there are other enemies on line. Though, if I happen to chance by him again, then I'll try to kill him again.

If I kill someone in a really close fight, then I'm less likely to avoid them than the person in the example above, whom I totally smoked.

If I kill someone and take a significant amount of their gear, presumably because I can use it, then they drop to the bottom of the list.

If I kill someone and full-sac them, then it's probably because I really, really detest that character. In that case, they probably retain their position at the top of my list, and are due for another full-sac next time I kill them.

There's maybe...two characters in the last year who I would give that treatment, and both of them were/are played by the same player.