A coffee aficionado who demands quality and shuns the use of flavored syrups and the practice of diluting espresso with copious quantities of milk; will only drink an espresso, a macchiato, or a cappuccino. Usually the least happy customer in today's marketing-driven specialty retail store.
A purist is one who desires that a particular item remain true to its essence and free from adulterating or diluting influences. The term may be used in almost any field, and can be applied either to the self or to others. Use of the term may be either pejorative or complimentary, depending on context.