It's not hard... just... frustrating at times. Relaxed it can be a pain in the ass to dismember. If you don't want to use grab to break it I advise hitting it either dead on and hard, or use the edge of something to cut it, like the corner of the hand.
With grab though it can be easy as pie. Just a little flick of the wrist can break it easily.
Either way, a hand is the easiest way to dismember anything really. So use them. Also, think brutal real life. Slam the side so that if you hit it that way in real life, the guy would be in srs pain. (backwards elbow)