3. Thrill of hunt
Basically it stuns them and knocks them back. Hold down your Bola and keep tapping your Impale button. I've stunned all three barbs at once and the AOE for Bola stuns and kills them at the same time. Seriously it really pisses them off.
You can stun them even more if you use Caltrops but I'd rather use other skills to up your dps instead.