A court might decide that the example of "irrational discrimination" is refusing to hire red-headed people for manual labor.
This form of discrimination does not have a logical or reasonable basis, as the hair color of a person has no relation to their ability to perform manual labor. The other examples involve considerations that may be seen as more legitimate or justifiable (e.g., citizenship requirements for government jobs, safety concerns regarding children in hazardous work, and legal exemptions regarding an elderly person's eligibility for the draft).
Thus, the refusal to hire individuals based solely on a physical characteristic like hair color would be seen as arbitrary and lacking a rational basis, exemplifying irrational discrimination.