I’m thinking more along the lines of Orsen in Lodoss Wars (posses by an anger spirit, has some sort of trigger) that sets them off.
Ideas? 
In Kill, Capture & Drive Off conflicts you have the weapon Berserker Rage: +1D/+1s Attack, -2D Defend; treat Feints played against your Attack as a Versus test and being disarmed applies the Exhausted condition.
I think Jared put together a Barbarian that used the Angry condition to get bonuses…
Also: the Skinchanger, which i’ll repost…NOW!
You’re a fierce hunter-gatherer from a primitive society. Be it from primordial energies, malevolent curses, magical potions or feral unions, you possess a mystical link with the world of beasts. Over time, you will learn to channel their abilities and take their forms. But as your power grows, so will the madness within.
Raw abilities: Distribute 8 points between Will and Health; Health may not be higher than Will.
Skills: Hunter 3, Fighter 2, Mentor 2, Scout 2, Scavenger 2, Survivalist 2
Special skill (choose one at 3): Criminal, Haggler, Pathfinder, Survivalist
Trait: Bestial—Even when in human form there’s something not quite right with you. Your nails and teeth are sharper, you stature is hunched, your arms and legs corded with ropy muscles. Your eyes gleam with feral light and you lose your temper far, far too easily.
Weapons: Dagger, battle axe, hand axe, spear, shield, bow, sling
Armor: None
Level benefits
Level 1
Skinchanger: You may wield primitive weapons (dagger, battle axe, hand axe, spear, shield, bow, sling). You wear may not armor or helmets. You possess one animalistic feature stemming from your Bestial trait.
Level 2
Savage: While angry, you may attack unarmed at no penalty. You may use your Bestial trait even when angry.
Catlike: You able to move swiftly, surely and silently through the wilderness. +1D to tests involving speed, stealth or balance.
Level 3
Fury: When angry, your unarmed attacks are at +1s and your armed attacks are at +1D.
Awareness: Your senses become preternaturally acute, giving you +1D to any test involving perception (such as scout tests to spot ambushes, hunter tests to track game, etc).
Level 4
Berserker: While angry and facing an opponent with a higher Might, increase your Might by +1.
Soul link: Test your Will against a beast’s Nature. If successful, you wrest control of its body while your body slumps into a comatose state. While in control of the beast, you have its Nature, descriptors, Might and weapons. You may only test using the beast’s Nature while in this state but you may not gain passes or fails. You may return to your body at any time but this severs the link. While comatose your human body is still susceptible to the Grind but your “borrowed” beast form is not. If you die while linked, the soul link is severed and your own soul is left to drift away, bodiless and forever lost.
Level 5
Shape of Rage: Choose a single beast form of Might 4+. Make a Health test with an obstacle equal to the beast’s Might to transform. If angry, you may immediately take on that form without making the test. Worn clothing is damaged during this transformation. While transformed, you have access to that beast’s Nature, descriptors, Might and weapons. You may return to human form at any time except if angry. Recover from angry by testing your human Will as normal.
Wild Shape: You may take the form of any beast with Might 3 or lower by making a Health test. The obstacle is equal to the Might of the beast. Whatever form you choose, you’ll gain access to that form’s Nature, descriptors, Might and weapons. There is no limit to the amount of time you may spend in this form but you may only return to human form after making one test.
Warning: While transformed you lose access to your gear, skills, human Nature descriptors and level benefits unless noted otherwise. Regardless of which benefit you choose, Nature tests in beast form do not advance human Nature — instead, successful tests remove passed Nature tests. If you have no passed Nature tests and you make a successful Nature test in beast form, your human Nature is taxed by 1. If your human Nature score ever reaches 0 while in your beast form, you are trapped in that form forever.
Thanks all! i didn’t think of 'rage when angry coniditioned…" still trying to disconnect Gaming from D&D 
One ability might be as simple as “Give yourself the Angry condition at will” or “Give yourself the Angry condition if/when…” and build off that premise.
Alternately, you could just make Berserker a trait and leave it at that.