I think it is pretty clear that a person can order a robot to destroy itself, and the robot would comply.
IIRC there is an example of this in the novel The Caves of Steel. There is a robot that had knowledge the murderer didn't want disclosed, and IIRC the murderer simply told the robot to destroy itself. The robot took some sort of radiation-emitting device and held it up to its head, scrambling the positronic brain.
We didn't see the actual command given. Probably "Robot, hold this thing up to your head and destroy yourself" would have been adequate. Certainly "Robot, a human being will come to harm unless you scramble your positronic brain" would have worked.
IMHO, Asimov's Three Laws of Robotics would not work in the real world. They are chiefly important because they marked the first time a writer even contemplated a framework of safety rules to keep robots from becoming a threat... before Asimov's robot stories, robots tended to be dangerous things in SF stories.
Asimov himself wrote a bunch of stories exploring the boundaries of the Three Laws. For example, in The Naked Sun, someone pointed out that you could put a robot brain in a spaceship with no crew on board (a purely automated spaceship) and tell the robot brain that all spaceships are machines with positronic brains, and any radio broadcasts from other ships are untrustworthy... then you would have a robotic space ship that would be able to destroy other space ships despite the First Law.
Other authors poked at the Three Laws in stories. The one I remember best is "A Code for Sam", where a Three Laws robot is miserable because the Three Laws are impractical in real life. (Example, a human is smoking a cigarette, and the robot feels it must keep the human from harming himself, so the robot must take the cigarette away from the human; but both human and robot are distressed.)
http://en.wikipedia.org/wiki/The_Three_Laws_of_Robotics_in_popular_culture
There is a really excellent web comic called Freefall that is actually a hard SF story and which has been exploring the issues surrounding robots and the laws under which robots operate. One of the main characters, perhaps the main character, is Florence Ambrose; she is an uplifted wolf, and legally her status is exactly like a robot (they refer to her as a "biological AI" or just an "AI" sometimes). In the Freefall comic, there are about 20 thousand humans living with about 450 million robots on a world that is being terraformed.
At one point, Florence discusses hierarchy of command: if the Mayor of the town ordered the robots not to destroy themselves without a good reason, then an ordinary person would be unable to countermand the order. Florence suggests making a temporary position that outranks all other positions, then having the person in that position give the robots new orders that in effect give them basic rights. The position could always be re-created at need, if any of the new orders turned out to have problems. It would cut down on abusive treatment toward the robots.
http://freefall.purrsia.com/
The human woman in these three comics is the Mayor. I think the planet just has the one city, so she is the highest-ranked government official on the planet. Also in the room are Florence (the uplifted wolf), and the Mayor's intern.
http://freefall.purrsia.com/ff2200/fc02137.htm
http://freefall.purrsia.com/ff2200/fc02138.htm
http://freefall.purrsia.com/ff2200/fc02139.htm