Wow...in the US I don't think this is the case.
I'm no lawyer but from my readings on self-defense law if you threaten me and I believe you are in a position to carry out that threat, I would be justified in defending myself.
Example 1: We are both at a party and you've had too much to drink and aren't feeling well. As you lay on the ground holding your head in an attempt to keep it from exploding you say "if you touch me I'll kill you". No threatening actions and I would doubt you had the physical ability to carry out the threat so I would not be justified in using force against you.
Example 2: You are walking toward me in a menacing manner with your hand in your jacket pocket and you threaten to kill me. From my readings I would be justified in using force against you even though you had not physically attacked me (yet).
It all comes down to whether I can convince a judge/jury that I truly believed my safety and/or life were jeapordized.
Again, I ain't no law person this is just what I've gathered in my reading.