"Dress codes" are pretty much "history" on all the major mass market lines. However, it's been quite some time since Carnival made theirs the most "relaxed".
They began allowing shorts in the dining room on non "formal nights" some time ago. Then they changed their "formal nights" to "elegant nights".
Once they did allow shorts in the dining room, I tried it out in the dining room, and guess what... it was fine.
I've worn them on several cruises over the years since then, and I've felt fine, and really don't think I've ruined any meals.
Basically they've said, if you want to dress up, feel free; if you don't feel free. But, don't expect others to dress the way you choose to.
I used to be one of the dress up crowd. Now I admit to enjoying relaxed and at ease.