As you can below, men are now able to wear shorts in the dining room for Cruise Casual nights...This is from the Carnival Faqs page.
Have a great cruise.
Cruise Casual Dining Dress Code: Gentlemen - Sport slacks, khakis, jeans (no cut-offs), dress shorts (long), collared sport shirts; Ladies - Casual dresses, casual skirts or pants and blouses, summer dresses, Capri pants, dress shorts, jeans (no cut-offs).
Not permitted in the dining room during the Cruise Casual dinner for ladies and gentlemen: shorts, gym shorts, basketball shorts, beach flip-flops, bathing suit attire, cut-off jeans, sleeveless shirts for men and baseball hats.
Cruise Elegant Dining Dress Code: Gentlemen - Dress slacks, dress shirts. We also suggest a sport coat. If you wish to wear suits and ties or tuxedos, by all means we invite you to do so. Ladies - Cocktail dresses, pantsuits, elegant skirts and blouses; if you‘d like to show off your evening gowns, that's great too!