As has been intimated above, you're automatically assuming that one that rides a bike is a) in to good health, and b) in to preserving the environment. While this may be true in a lot of cases, one does not always beget the other.
In the early 90's I recall seeing a guy riding in full kit and smoking. Then (as now) it tickled the irony meter (thus I'm guilty of making that same logic jump, as well).