Are we talking just a much-repressed part of your own nature, or somebody else entirely? Because that'd be kinda scary, I think.

I think I might have one too, or at least I'm not sure because if I do, mine's awful quiet. But I'll be trucking along and every now and then something will make this fierce protective urge jump out, and in the most menial of circumstances, somebody might jokingly malign a group I'm affiliated with and then all of a sudden I just get mad, but very calmly mad, sort of a quiet boil like a tiger who hasn't bared her teeth yet or a swordsman who hasn't pulled out his sword. Or every once in a while I'll just get these feral moods where I want to stalk around and snarl and hold my hands like claws. It calms itself down whenever I get to do a lot of physical stuff, like starting to haul pallets. Nothing quite so pronounced as yours, of course, or maybe I just learned to repress it really well.

Berserker urges, now that is a little frightening.