As other people have said, this is workplace harassment and you don't have to take it. I had a similar situation where a security guard who mocked my stutter. I was new at work and was worried about making a bad impression by going to HR so soon after starting. But I realized that I need to not stand up for myself and anybody else he might be mocking, and I went to HR. He was gone a few days later. It turned out that he had had other complaints against him prior and my complaint was the final straw. Stand up for yourself.