Is it illegal to say "if you do [insert negative action], I will kill you." to someone?

I have been unable to find websites mentioning the legal difference between an illegal treat and a warning so. I have no idea where the law separates warning, angry ranting, and a true threat. Elonis v. united states didn't make it easier for me to know for sure where the line is. Examples of what I am asking about are below. Thanks ahead of time. Examples: "If you throw my Samsung Galaxy S6, I will kill you." or "If you call me fat again, I am going to F-ing kill you. or "If you EVER cheat on me, I will kill you." Another example is: "If [persons name] talks to [another persons name] like that again, I am going to murder him."