What is the ruling on not respecting the mosque's imam?

Among a Muslim's rights upon his brother are respecting him and not belittling him. Honoring scholars and people of virtue, especially, is part of glorifying Allah. Mocking or ridiculing them is a characteristic of hypocrites. Ridiculing scholars is of two types: The first relates to their persons, which is forbidden. The second relates to their being scholars or to the knowledge they possess, which is disbelief (kufr) because it is ridiculing the religion and knowledge. This necessitates repentance; otherwise, it is apostasy deserving of execution.