preach to the choir

Nikon choir

A large group of photographers simultaneously capturing images of a celebrity, producing numerous photographic flashes along with an accompanying din of clicking camera shutters.

preach in the desert

To speak to or persuade a nearly nonexistent audience, or to an audience not listening.

preach to deaf ears

To attempt to persuade a party that does not wish to listen or cannot be altered in its conviction.

preach water and drink wine

To act hypocritically; to fail to practice what one preaches.