In retrospect, Charles thinks he should have realized what it meant when Erik left the helmet on the White House lawn, but perhaps he can be forgiven for the oversight, considering the fact that he had spent the previous twenty minutes trapped beneath part of a football stadium (fuck you very much, Mr. Lenscherr).
It's not until they get back to the mansion two days later and Hank shuffles nervously into his study holding the blasted thing like it's a live bomb and asks "Um...Professor? What should I do with this?" that Charles even registers that Erik hadn't taken it with him when he left Washington.
He stares at the helmet mutely, long enough for Hank to start that awkward toe-tapping thing he does when he's anxious, then manages to say something that sounds like "leave it here, I'll deal with it."
Hank drops the helmet faster than a live coal and makes his escape. Charles is a lot better than he was just a month ago, thank God, but if anything, his metal-bending...thingy (Hank honestly doesn't know how to classify Erik's relationship with the professor anymore) is a touchier subject than ever.
Back in the study, Charles looks at the helmet. The helmet looks back at Charles. No, that's ridiculous. The helmet can't look, it's an inanimate object, get ahold of yourself Xavier. Nevertheless, he can't erase the memory of cold grey eyes sparking in contrast against the dull metal, the same eyes that had once softened with warmth over a chessboard beside a crackling glow, that glistened with tears as together they unearthed the buried gems within a dark mind — stop it Charles, stop it right now. He shoves the wretched bucket, and the memories it summons, away, as though physical distance will somehow lessen the ache. It's a physical manifestation of everything broken between himself and Erik; why the hell did Hank take it along. Why couldn't he have left it to be picked up and melted down with the rest of the debris from Erik's little 'statement' dammit?
But... why did Erik leave it behind in the first place?
Charles dismisses the thought as quickly as it appears (he's become quite good at that in the past decade). Erik probably forgot about the helmet; he had just been shot through the neck after all, and even with a telepathic boost to get him on his feet, that kind of trauma is bound to leave one's brain a little woozy. Yes, that must have been it.
Charles wraps up the helmet in an old blanket that reeks, rather embarrassingly, of alcohol. Then he puts the bundle in a box, and just to be safe he puts that box in another box. He briefly considers a third, but he's out all of boxes, so with more ripping and grunting than is strictly necessary, he seals the whole thing up with tape. Belatedly he realizes that an entire roll of duct tape is probably somewhat extreme, but can't bring himself to care.
"Serves you right, you little shit," he mutters, not sure whether he's addressing Erik or the helmet, and writes "TACKY AS FUCK" on the top in lieu of a label.
When Hank returns an hour later and sees the professor's little project, he wisely refrains from making any comment beyond asking if he ought to put it upstairs with the old equipment. Charles is muttering to himself from the sofa and doesn't reply, but Hank, reassured by the absence of any empty bottles, takes this as a yes and leaves with the (surprisingly large —the helmet's not that big) box.