Pew Pressure 

The phenomenon that occurs in a Catholic Church when someone stands at the wrong time and the rest of the congregation stands up too. This usually happens because no one really knows when to sit, stand, and kneel so they copy those around them.

This phrase comes from the commonly known phrase "peer pressure".

Mrs. McCreedy accidentally started to stand up during the blessing of the body and blood and was going to subtly sit back down, but, to her horror, those around her succumbed to pew pressure and were starting to stand up too. She was forced to stand up the rest of the way because she didn't want to be the only one still sitting.

Pew Pressure by Kalupe January 18, 2011