A more thorough explanation:

McNary comity is a principle that says a U.S. district court should not hear a taxpayer's civil-rights challenge to the administration of a state's tax system. This means that if a taxpayer has a complaint about how their state is handling taxes, they cannot take it to a federal court.

For example, in the case of Fair Assessment in Real Estate Ass'n v. McNary, a group of taxpayers sued the state of Arizona, claiming that the state's property tax system was unfair. However, the Supreme Court ruled that the case could not be heard in federal court because of McNary comity.

Another example could be a taxpayer in California who believes that the state's income tax system is discriminatory. Even if they file a lawsuit in a federal court, the court would likely dismiss the case based on McNary comity.

Overall, McNary comity is an important principle that helps to maintain the balance of power between state and federal courts when it comes to tax issues.