I don't see what's impolite or unreasonable about that. I really do think the name is stupid, and I really would be prejudiced against a company with a name like that.
I suppose I could have said the name is "suboptimal" or something but why beat about the bush?
You could try couching it in some politeness: "The idea looks good, but my honest opinion is that the name sounds awful". Also, keep in mind the "what would you say in person" guideline. I guess some people would be that blunt in person, but for most people, it puts things in enough perspective to produce something polite.
I suppose I could have said the name is "suboptimal" or something but why beat about the bush?