This is outdated English slang of uncertain even era of currency. The example given in The Word Museum: The Most Remarkable English Words Ever Forgotten by Jeffrey Kacirk is, "If one female sits too close to another as to rumple or crease her dress by pressing or sitting upon it, she is said to miscomfrumple it," supposedly from Northamptonshire, quoting a circa 1900 English dialect dictionary -- so a guess of 18th century is as good as any. It's also unknown origin of course, though clearly "rumple" had something to do with the matter. But all that's irrelevant in the face of just how fun it is to say. It's one of those words that sounds like what it means.
They said they'd spent the whole time studying, but I saw how the bedsheets were miscomfrumpled.