While spectating another predator hunting a ravager in single combat, I witness a spitter in the distance hit him with some acid, this marks him (and the ravager, if this was coordinated between them) as unworthy prey, and as such I would be ALLOWED to dispatch the them in whatever way I please. Due to my character story, I probably wouldn't just blast them to pieces though, preferring a more personal experience.
I could go to the forum and list the reasons to mark someone as dishonorable prey, but I don't know if that would really prove anything.
Another, more interesting approach would be to use the combination of cloaking and plasma weapons as a method of instilling fear, when combined with the predators great speed, I could fire a shot (harmlessly in the wall) from an adjacent room from a squad of marines. Maybe changing positions and repeating, to make the illusion that I'm not alone. Both as a marine, and as a player, I would be quite nervous knowing that a group of predators with their plasma pistols at the ready are stalking my squad. and as a predator, their reaction would be a great opportunity to measure their worth as prey.
And of course the rare case of an abomination. All bets are off with those things.