SeriousIssues said:
Anime DOES kinda suck. So he's right.
Why does anime suck?
Death Note has a more sophisticated and interesting story than 90% of the live-action TV shows out there.
If you want to trap him, sit him down and watch the Death Note live-action films with him. Then when they're finished, go bring out the manga and anime versions and tell him that that movie he just watched was a simplified and dumbed-down adaptation of that. Maybe put on the anime and show him part of it.
I can't vouch for cosplay, I can't relate to anything more complex than wearing a robe and wizard hat to the Harry Potter premiere (and even then, I'd never have done it myself).