Interesting. I don't find the term to be in the least bit offensive, just hilariously inaccurate. I honestly don't know a whole lot about Darwin as a person; most of what we know about evolution now has little to do with his own personal research, anyway. It's as if antagonists think the modern theory of evolution hasn't moved forward since the man passed away and adhere to his ideas blindly without the benefit of any further research. Quite strange.
Naming a movement or doctrine after the man who founded or led it often has pejorative connotations. The suffix "ite" has a similar usage: Luddite, Millerite, etc. Thus, some creationists also use "Darwinite."