As John has demonstrated on a few occasions, he doesn't actually have any nice clothes, just shirts that have buttons, which is what he's wearing now. He arrived early but loitered at a distance until Erik and Charles arrived, and followed them in, saying as little as possible to either of them. If Charles happens to notice the little telepathic facade of calm normalcy the Stepford Cuckoos stuck in his head, meant to serve as a tarp covering what would be a roving tank of various plans of terrorist action, well... that can't really be avoided. And doesn't even matter, right? They're all on the same side. Right now. (That's just another thing he really does not need to be thinking right now.)