My husband wore a dark navy sports jacket, shirt and matching tie, and dark olive dress pants on one of the formal nights of our last cruise. On the other formal night he used the same jacket, different shirt and tie, and a pair of dark grey pants. He looked awesome! I think as long as you look "stuffy" and formal you will fit right in. The sports jacket is the best investment he has made....so versatile..and he feels comfortable in it. That is what is important...feeling comfortable! Don't worry about a tux, unless of course that is what he wants to do!