An excellent article with that subject line can be found over on Slate. An excerpt:
Though most Americans don’t ride bikes, bikers are less likely to stereotype drivers because most of us also drive. The “otherness” of cyclists makes them stand out, and that helps drivers cement their negative conclusions. This is also why sentiments like “taxi drivers are awful” and “Jersey drivers are terrible” are common, but you don’t often hear someone say “all drivers suck.” People don’t like lumping themselves into whatever group they are making negative conclusions about, so we subconsciously seek out a distinguishing characteristic first.
Every time another bicyclist pulls some dickish stunt, the affect heuristic kicks in to reinforce the preconceived biases. The same isn’t true in reverse: The conviction that bicyclists are erratically moving hazards is not diminished by the repeated observance of safe and respectful riding. Facts and logical arguments that do not conform to the emotional conclusion are discounted or disregarded. But we’re not doomed to our initial prejudices: Once a person becomes aware of her biases, she is more able to engage rational thought processes to overcome the affect heuristic and dispel her inaccurate conclusions. So, study those stats bike haters!