To mess something up or disarrange it is to rumple it. Even if you make your bed neatly in the morning, your dog might jump up and rumple it as soon as you leave for school.
When you take something smooth or neat and make it wrinkled or crumpled, you rumple it. A dad might have the annoying habit of always wanting to rumple his son's perfectly combed hair, for example. And if you fall asleep in your tuxedo, you'll rumple it too. Experts think that rumple started as a variation on the now-obsolete verb rimple, "to wrinkle."