Again it's a Haruhi-chan related joke. During a super secret Brigade meeting to discuss what to do about April Fools Day -- a day Koizumi alleges that Haruhi's powers make all her lies a reality -- they each wear masks with their various positions/secret identities during the entire thing.
Translation revised, but I'm still not sure I'm interpreting the exchange in the top panel correctly.
You really went all out making these props.The two of us made them at Koizumi-kun's house last night, so it wasn't that bad.You wrote on all of these?I helped too!It must have been rough making so many.Ordinary PersonWhen on Earth did you have time?...Ohh, did you now?Well, I like to do all things with a sense of style.