Obsessive Compulsive Disorder, It is when you can not help having certain things in a certain way.  For example; OCD like keeping colour objects of the same colour together.  They will tend to do the opposite of what you want.  If you want a Lot of Apples in one room a few in another room.  But they will do the opposite and put few in the first room and Lots in the second room.  It is quite complicated.  And in your case you are obsessed on Bud without his hat.