Tell him he's "Dressed By the Internet."
How to do it: "Sweet kit, bro. Where'd you reblog it from?"
The Internet is a great tool for making guys aware of trends and brands, but plenty of dudes take it way too literally. The point of personal style is to dress in a way that reflects who you are, not regurgitate everything you've read. Accusing someone of being "dressed by the Internet" is like telling someone they're painting by the numbers.