As a lawyer, it's important to really remember one thing: you're a lawyer and your conduct while lawyering and while not lawyering matters because it reflects upon the profession as a whole.
To that end, lawyers really can't threaten violence or much else besides legal action (pending exceptions), and doing so can often be more than just an ethics violation. It could very well be criminal. One lawyer learned this lesson the hard way when his emotions clearly seem to have got the best of him while he was a party in his child custody case.
Don't Threaten Lawyers with Violence
Simply put, threatening violence, pretty much everywhere, is a crime. Often it is a crime that is not taken seriously, even when the credibility of the threat is unknown, but if you're a lawyer making that threat, law enforcement might expect you to know better.
In the above mentioned case of Brendan McLeod, his direct threats were much less clear, but did seem to imply violence. He told one lawyer that he would "strap one on you" and told another "I will come find you." And while these statements in isolation might not be so menacing as to warrant arrest, McLeod allegedly told a third party that he was going to kill the two lawyers involved in his child custody case.
Good Lawyer, Emotional Parent
Although McLeod seems to have let his emotions get the best of him as a parent fighting for custody of his child, apparently he's a pretty good lawyer and is still practicing while fighting criminal charges over making those threats. Recently he secured an acquittal on murder and burglary charges for his client. Unfortunately, while the charges are pending, he must notify the local sheriff's office before making any court appearances.