Hell, go one step further. Buy something you can't believe anyone would want to buy in the first place.
Whether it's a somewhat unsettling-looking bust of Legolas or a goofy demon statue or a "Hellboy" necktie, chances are, there are entire tables of truly absurd objects that a friendly chap with long hair and a beard will be all too happy to peddle to you. The point is not for the enjoyment of the object itself, it's to get into the strangeness of it all, and support the culture. You're sure to have a story to tell when someone asks where, exactly, you found a "Buck Rogers" handkerchief.