So, I've heard that it a hit from a hammer while it's burning provides sufficient shock.
As far as the fumes go, we got to rig some charges when I was a cadet, and the stuff has a very chemically smell to it. Anything that smells like that in its stable form would have to release some nasty fumes when it's burned.
I handled C4 for about a decade in the Army. Would I recommend playing f@ck around games with it? No. However, C4 isn’t going to detonate in the way you described. It’s stability is it’s best feature.