In the Predator movies, they were shown to be quite ruthless, killing simply because they got a kick out of it. If there was no challenger they deemed worthy enough, why would they waste their time?
In AVP, the "blooding ritual" gave the impression that this particular clan at least had some sort of ceremonial back ground or code, killing aliens to gain respect from their peers. But I've always liked the thought that predators in general operate in a very grey spectrum between honourable & psychotic. They hunt for sport, but as to whether they truly have a "code", that could very well be up to each individual predator's morals or beliefs.
