You can dress as over the top as you'd like, but there are restrictions when it comes to how casual you can go on formal night. Jeans, men's sleeveless shirts, shorts, t-shirts, sportswear, baseball hats, flip-flops, and swimsuits are not permitted in the dining room when the evening's attire is "cruise elegant." Depending on the duration of your sail, your ship will either have one or two formal nights.
Image Source: POPSUGAR Photography / Nicole Yi