Hey Warheart, tell him to go and dress however the hell he wants. I've seen Bodom 5 times now, and everytime I go in almost all Abercrombie clothes (because I work there... well, used to) and I have never had a problem with anyone. CoB has been my favorite band for almost 6 years now, and I've listened to metal music for prally twice as long. It doesn't matter how you dress.... if you like the music and are a CoB fan, then go regardless to what you look like. If anyone gets in your friends face about it, tell'em to fuck off and that your there to enjoy the show. If they can't accept that because they're "hardcore" or "METAL!" then tell them to go play with their cock piercings or braid eachother's hair. The true CoB fan's will back you up anyway.
Enjoy the show man, CoB blow me away every time i see them.