There are many problems with this myth.
One is that "atheists' is a group and a statement like that should have been backed by at least some form of consensus survey. Being a myth, that obviously has not been done.
Second is the adjective "superior" which is a relative position, superior than what? The implicit comparison is of course towards the opposite of the term atheists, i.e. people who believes in an imaginary god. In this case, I think this statement may be true and valid. Evidence, logic and reason based thinking has obviously advanced the life of human in more than one way. Historically, faith-based thinking has hindered scientific progress. Most atheists do no base their thinking and decision on faith (that's the definition of atheist, I suppose) while religious believers do. Hence, as a group, atheists, is obviously superior in decision making than the comparative group - believers of unproven ancient stories.
"Atheists think they're superior" implies arrogance. Religious evangelists tell people to believe in their imaginary god, it is called "spreading the gospel". When atheists are presenting their ideas and demanding evidence for the existence of god, it is labeled as arrogance. Let see who is more arrogance in the following clip.
Richard Dawkins was obviously angry. I would be too if I was in his position, wouldn't you? But who was arrogance?
OK, Ted Haggard is not representative of evangelists, you may argue. Well he was the chairman of evangelicals until his more interesting private life was exposed. [The follow clip repeats some of the above clip.]