First of all, a bit of background- from my point of view (and I've seen this from several autistics out there, so I'm by no means alone in this) NTs have either a myth or a special power that us autistics simply don't. That myth/special power goes by many names: Empathy, Telepathy, "appropriate behavior", reading "body language" and "tone of voice". It might exist, it might not. I've never quite convinced myself that it exists. But a HUGE portion of the behavior of lower functioning autistics that I've been in contact with is based on the assumption that it both exists & they don't have it.
Us autistics try to make up for it in different ways. Myself, I listen closely, and try to limit my communications to text/telephone whenever possible- this seems to at least limit the effect based on it. Lower functioning children I've seen try to replace this power with various senses- touch, taste, smell- without success of course, but at least they try. My own theory on why autistic children seem to "regress" in verbal ability despite having, in writing, a large vocabulary is due to simply giving up and assuming that everybody else already knows what they know- so why bother expending energy in talking.
Karen mentioned the frustration apparent at "not being able to talk". I'm going to suggest here a possible alternate explaination: not realizing that communication hasn't happened, the child gets frustrated at your apparent refusal to understand. Not inability to understand, but "refusal" to understand. It doesn't matter one whit that the child's logic and "theory of mind" is wrong in blaming you, that is the facts from his point of view and that's where his anger is coming from.
One of the potential causes of autistic behavior, of course, is the inability of the brain to process all the information coming in from the five senses. I know I myself get massive migraines from the mere attempt. Here's what I suggest for an autism inspired tantrum based on miscommunication, and I know it's going to sound 19th century to some parents: Create a room in your house specifically for your autistic child. It doesn't have to have windows, it might be no bigger than a closet. In fact, it might *be* a closet. In this room, there should be a computer with network hookup, some form of white noise/music generator, fully adjustable lighting, and a comfy chair or bed. Maybe a solartube with a shade. A refuge from the world, so to speak. When a tantrum happens at home- put the kid in the room and leave him alone for at least an hour. When out and about, return home as soon as possible, and put the kid in the room.
Eventually, he'll come to his own terms with whatever caused the friction. But to come to those terms, he needs time, and the ability to control the stimulation of his environment to the smallest degree.
And that's just a small view, from the inside of an autistic brain. Give it what authority you will, I don't care and remember that I may indeed be sane, as defined by the first post in this blog.