Doctors are generally a busy, motivated, and well-respected group of professionals. Then they retire. While the loss of stature may prove difficult, a few amusing gifts might make the transition from medical authority to aged humility just that much easier.
The doctor you want to give a gift to may have assisted patients with their mobility. Now you can assist the soon-to-be-retired physician with his own movement by giving him an inflatable "over the hill" walker. (See Reference 1.)
The retiring doctor may not be giving any more injections, but no one else has to know that. These syringe-like pens will help a retiring doctor maintain her professional image. (See Reference 2.)
A doctor's mind is full of thoughts about disease and contagion, and now he can keep those morbid thoughts near his heart with any one of these disease-themed ties. (See Reference 3.)