Yeah ultimately it comes down to just you being sensitive. There is no rule regarding offensive names that I'm aware of.
No, there aren't any rules against "offensive" usernames, and I'd argue that Theymos would probably never implement such a rule given how subjective offensiveness is. Personally, if I just came across a post by hitler420 I wouldn't think anything of the moniker. Jesus, if your fur gets ruffled by the mere mention of a word or name, you really need to grow a thicker skin. There aren't any safe spaces here on bitcointalk.
Of course its a stupid name, but the only thing he's really harming are his chances of anyone taking him seriously.
See, I don't think it's a stupid username or a good one or clever or anything at all. I wouldn't judge that person by what he chooses to call himself on the forum; I'd judge him on the quality of his posts and that's it.
This isn't the place for people who get offended easily. OP, you've been here since 2016 and you ought to know that.