When the flight attendants are on hidden camera at the detectives' apartment, one of them says that when Brenda says "Thanks you very much" she really means "You can stick it". Then the shot cuts to Brenda who pushes her glasses up using her middle finger, subtly "flipping off" the monitor where they're watching the video.
This is considered another "Flynn and Provenza" episode, where they do something foolish and caused a big problem for everyone.