For all we know, phasers are personally encoded to the thumbprints of their current user, and nothing else will cause them to fire. When do we witness a situation where a villain would get hold of the phaser of the good guy and use it against its former user?
(In ST:FC, Lily Sloane does grab Picard's gun, but there's no reason to believe she could actually have fired it: Picard has every reason to pretend that Sloane really poses a threat to him, because that will calm her down. In certain other circumstances, the person grabbing the gun would be well trained in phaser operations, and would know how to rapidly reset the ownership of the weapon.)
Of course, there are downsides to a gun that has a mind of its own and the authority to refuse from firing. Could you really trust your life on such a weapon?
On the issue of pointing a hand phaser at a non-target, we probably have to consider that phasers seldom fire exactly where they are pointed. That is, almost all the phaser beams in TOS are shown to be off-boresight, at an angle to the "barrel", and many of the TNG beams are that, too. Perhaps the general direction where the emitter head points is not particularly important, and only the movement of the user's thumb on the triggerpad will point the beam to the desired direction?
In that case, a phaser pointed at your buddy's chin would be as harmless as a whip or a morningstar held under his chin: it wouldn't really be pointing anywhere, not until the operator initiated the complex set of movements that gave the weapon its power to do harm. There's no such thing as an accidental discharging of a whip (although there may certainly be accidental misaiming of a whip!), and there might not be such a thing for phasers, either. The beam would be "flaccid" until specifically thumbed to the direction of the target.
Timo Saloniemi