this cab driver will remain "stupid people" unless and until he is educated otherwise.
One with CF should not feel shame in educating - spread the word and we will get more funding for research programs. Why is CF such an unknown, whereas breast cancer, aids and leukemia is all over the media? Common people.
If you feel ashamed when you cough, the people around us have nothing to go by, but our fear, so they will back off - you then have created your own dilemma
How about even something as simple as "My cough is due to a disease I have, not due to something you can catch"
Carry some small brochures with you perhaps.