Depends on what your interactions with him are like.
Nazis and their ilk often love getting challenged, because it gives them a chance to grandstand and some of them are good at winning debates (or appearing to). If you can get away with just not interacting with the guy, that's probably the way to go, for your own sake
If that's not an option, I'd go to HR or a manager or whatever you've got in your workplace and tell them you don't feel comfortable working with Mr Nazi. If you've got some sort of proof of his views, they might just fire him and solve the problem that way.
I was briefly in an office environment where one guy didn't want to be around another guy due to opinions he held (among other things). Our manager was sympathetic and worked out something that both kept the peace and made the first guy happy, but she actually cared about her employees, which seems like an uncommon situation.
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