Wow...in the US I don't think this is the case. I can talk all kinds of trash and make all kinds of threats but unless I take steps to actually make it happen, no verbal threat that I'm aware of can be regarded as an attack warranting violent response......words alone should never provoke physical retaliation.
Both in the UK and the US, you can defend yourself against a reasonable belief you're immediately going to be attacked. Quoting a random google'd legal page:
There must be an overt act by the person which indicates that he immediately intends to carry out the threat. The person threatened must reasonably believe that he will be killed or injured if he does not act immediately.
That can be pulling back a punch, or picking up a knife or an aggressive physical move. If I sit in an armchair and say "I'm gunno slap your face" I haven't handed you the right to break a chair over my head.
Even in the various cases where battered women have killed/burnt alive their sleeping husbands, self-defense is not a workable plea as there was no imminent danger - self-defense has to be an act to avert a danger *now*.
(My understanding of this law comes from the UK, although all the web references I found in a couple of minutes of looking were from the US).