need help!

I'm frightened, scared, confused...ended a relationship with a N I work with when I found out he was cheating in perverse ways. Texted him when I left his house that I wanted no contact from him anymore. My story is so typical of those on this forum...mine was so caught up in voyeurism, cheating, porn, etc, but he could never admit fully to it.
Been almost 2 weeks NC...I know he is probably shocked I haven't contacted him because I would always come running to 'fix' the problem. When I was walking into work on Thursday, I crossed his path outside. He dripped venom and sarcasm, trying to engage me, saying GOOD MORNING (but VERY venomous and sarcastically) HOW ARE YOU?? and then when I kept walking and ignoring, he seemed even madder and more venomous, and yelled WELL THEN YOU JUST HAVE A WONDERFUL DAY THEN!!! and I could tell he was extremely pissed off. It scared and embarrased me, wondering who else heard this...I was too afraid to turn around and wanted to ignore.
Should I have?? I'm thinking I need to address this with HR to get him to stop, because I'm sure he'll do it again. He's normally a quiet and silent treatment type. Don't want to go through it at work, but he texted me when I left 2 weeks ago that if I said anything at work about what had happened that I would get it "ten times over". Should I tell him if he doesn't stop that I will get work involved? I know he's afraid people at work will find out he engages in perverted acts and more about our time together (8 months) and it doesn't have to be discussed, but I just want this to stop so I can concentrate on my healing...please help!!! He's not a kid, in his late 40s...don't know what to do and stressing terribly, sick to my stomach and afraid it will happen again....!!