NTA - workplaces should carry an expectation of safety for their employees. No employee should ever be put in a situation where they feel threatened in terms of their safety. You did the right thing by reporting him. In the future, if he did this to someone else who reported it as a reason for quitting or feeling unsafe, it could be a serious liability for the company. Tom could have come and expressed his feelings to you in an appropriate manner. He didn't. If he is old enough to have worked there a long time, he is old enough to know better and know that cursing the boss is not a smart move. That, in and of itself could be grounds for being written up. Acting the way he did? He's lucky he still has a job. Most HR these days have a zero tolerance policy.