What does this mean? Absolutely nothing. I’m sure there are lots of nerds who own batman stuff.
What’s important and that’s being overlooked is that Holmes wanted to blow up his entire apartment building. Which should have happened, because he left with loud music playing and his door open. Someone was supposed to open the door to tell him to shut off the music, and blow the place sky-high, but that never happened.
So remember, Holmes didn’t just want to kill a bunch of random people attending the opening of a Batman movie, he also wanted to kill all the people he lived with in his apartment building.