As adjectives the difference between exceptional and stiff
is that
exceptional is forming an exception; not ordinary; uncommon; rare while
stiff is of an object, rigid, hard to bend, inflexible.
As a noun stiff is
an average person, usually male, of no particular distinction, skill, or education, often a
working stiff''''' or ''lucky '''stiff .
As a verb stiff is
to fail to pay that which one owes (implicitly or explicitly) to another, especially by departing hastily.