Am I overreacting, or should I report past workplace intimidation to HR?

He hasn't done anything since but I'm still anxious. He was staring me down on the way out like he wanted to fight one day. Sometimes he'll laugh really loud (if I'm the only one in proximity like he's mocking me) or say "pfft" or something really loud under his breathe. Am I overreacting or should I go to HR?
Am I overreacting, or should I report past workplace intimidation to HR?
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