No!!!
Robinpiper,
As far as the U.S. is concerned, the answer is a flat and simple "NO". Don't know about the rest of the world.
FAR Part 61 defines the requirements for 'learning to fly'. Many of the requirements for a 'student' cannot be met without a Certified Flight Instructor.
Now, having said that...you, yourself, as a private pilot, can take a friend along with you on a flight...and 'teach' some things about flying...but, as far as the FAA is concerned, your friend is not officially being 'instructed'.
Any FAA FSDO office can answer any of your questions.
PantLoad