Rationality, as Wikipedia says, is:
Rationality is the quality or state of being reasonable, based on facts or reason. Rationality implies the conformity of one's beliefs with one's reasons to believe, or of one's actions with one's reasons for action. "Rationality" has different specialized meanings in philosophy , economics, sociology , psychology , evolutionary biology , and political science.
That being said can the concept of rationality have any meaning when we don't have irrationality in a fictional universe; when all men with thinking ability, act equally rationally as any other?
How would we define irrationality in absence of irrationality?