You're saying those photos are real? Don't 'insult my intelligence'. [=don't treat me as though I am stupid; don't expect me to believe those photos are real]
Most people were forced to work longer hours each week, and to 'add insult to injury', the company decided not to give pay raises.
They're understandably 'insulted' when no one asks for their opinion on a matter that affects them so much.
(..) You're finished. I'm putting you on a plane to Vegas. Tom. I want you to stay there. Understand? Only don't tell me you're innocent. Because it insults my intelligence. Makes me very angry. Who approached you? Tattaglia or Barzini? It was Barzini. Good. (..)1972 The Godfather