Need help with a problem with a friend at work?

Today on of the guys I work with , said some very improper things and made a threat to do harm to me. I will try to explain quickly , my Friend is black and i am not , he started in about how all his problems at work are due to the fact he " has the wrong paint job" to put it as he likes to say, and how our boss is (used every word under the sun) and he is the biggest racist and etc. I replied to my friend that that is not totally true ( nice way of telling him he is talking out of his other end again) he got more upset and got in my face and told me that he wants me to tell our boss what he said and he will tell our boss a lot more and he will kick his A## and a lot more, I told him to relax and go for a smoke , he got in my fac and started in on me and saying he will kick my A## and with fists clutched and in a very threaten way, all this was seen and hear by others around , Should I just let this go into the past and not bring this to the attention of the bosses and /or HR, we just had cles and meeting on subjects like this and we where told to report things like that ASAP. As this was happening I felt very uneasy over this , threatened to a level, the problem is I do not want to get him in troubble and cost him his job, this was not the first time he "went off" at someone at work and if it was the other way around and some else did what he did he would go to HR in a heart beat over it . What do you think I should do just drop it and move on or follw what my company's policy states should be done? being ripped in half by this . Thank you