Charlie may not know Jehan that well, but he is Naomi's brother and he does seem to be having a pretty bad time with the angry girl brigade (one of its members being his sister.) Parties are always a good way to cheer people up and once he heard about it, he had spent a good amount of his time between his other hobbies at camp and made party hats.

Yes, party hats.

They're you're typical conical ones with little pom-poms on the tops and he's decorated each one by hand. As soon as he arrives, he's out handing them out to as many people as he can, including you sulking wallflowers.