A man was being prosecuted for some crime, and he got upset when his own lawyer said that she uncovered incriminating evidence that she was giving to the prosecution. He had good reason to be upset, as it is not the job of his defense lawyer to go fishing for incriminating evidence. He must have gotten even more upset when she called police, pressed charges for threatening her, and got him convicted and sentenced to 3 years in prison.
From an Illinois appeals court decision:
On the record before us, we do not see how it would be possible for any rational trier of fact to infer, beyond a reasonable doubt, that when defendant told Lacy, “‘I’m gonna get you,’“ he meant violent retribution as opposed to these forms of nonviolent retribution — one of which he had just got done discussing with her. In the absence of any evidence that could justify a finding, beyond a reasonable doubt, that defendant’s threat was a “true threat,” we reverse his conviction on the ground that it violates the first amendment, made applicable to the states by the fourteenth amendment.So you are entirely within your Constitutional rights to say “I’m gonna get you“ if you intended to hold someone accountable in some lawful way. But you might spend some time in jail before you get the attention of a sympathetic judge.
My suggestion is to say something like "I'm gonna hold you accountable for this" or something like that. But maybe even that is dangerous when dealing with backstabbing govt agents who have friends who are prosecutors and judges.