This is obtained in level one called Low Life/Low Tech
The Skinner appears halfway through the level. He is a larger enemy than the others you have fought up to this point. Fight him normally at first than he will go berserk. He will glow red and spawn some friends to feed off their power. He will charge at you periodically but to ensure he does more often stay a distance from him. When you here him grunting loudly or see a red exclamation over his head, dodge. You can get this after you wipe the other enemies out if you wish but he is more aggressive and attacks more often when he is berserk.