I, for one, am on vacation and refuse to own or rent formal wear. I was told the last two times that we were on MAriner that even on the formal nights, we were NOT required to dress formally, and that the normal casual wear for men was fine and dandy. We even had our pictures taken against the nice backdrops, with slacks and a polo shirt for me, and my wife's normal casual wear. I know, and understand, that there are other who like to dress up for the formal nights. I don't bug them, and they don't bug me. We're all on a cruise, so we all get to enjoy it at our leasure and pleasure.
Have a great time-you'll love Mariner.