Legal Question in Criminal Law in California

No way. If the threat is present and imminent, and is to 'right now' do bodily harm, and you in good faith reasonably are justified in believing they have the ability to do so, such as a weapon in hand, then and only then can you use necessary force to defend and prevent harm. Otherwise it is you who is the aggressor and likely to be charged with a crime like murder. Mere threats should be reported to police, not taken to 'self help'. You will then have evidence of the threat documented, and if you are prepared to defend yourself if it happens later, it will help prove you were justified in defending yourself.