I think he did the right thing, i think it showed his loyalty to Jack, and what Nikki did was cruel, you shouldn't set anybody up for humiliation
Danny went up in my estimation, and as i said in another thread, Marc has also blown Nikki's plan, so will he be classed as sneaky?
Marc is there to cause trouble and he knew Danny was going to tell Jack, Marc is hoping for fireworks, but will he get them?