How do you know they're using Cohen because of The OC?
There may be a few pop-culture obsessed people who did name their child after whoever the heck Cohen from The OC is, but probably more people use it to honor their heritage or a specific individual. Plus, as Hufflepuffer mentioned, innapropriate names are names that hurt a child or an individual. Naming somebody Knife, Aryan, Stalin or Hitler would fall under this category. Cohen does not seem that offensive compared to those names.