My rogue traders have either followed the clean-cut style, with Navy or other military style dress uniforms (sometimes adorned with accessories, including, but not limited to, the biggest spaulders reasonably wearable without integrated suspensors), and the full-on eclectic, including one who managed to obtain a Harlequin Holosuit, another who insists on going bare chested everywhere (he used to go out naked, but an incident with the Sisters of His Endless Misericorde made him somewhat more prudish in public), and one who always tries to dress as inappropriately as possible to any meeting, to destabilize his opponents.
However, what they all have in common is an obsession for having the best, most impressive headgear possible. You see, in my version of the 40k universe, it is a long standing tradition among Rogue Traders, first begun by the Emperor himself, that order of precedence between otherwise equal rivals be bestowed based on the impressiveness of their respective hats, as judged by all warrant bearers in assistance. This of course means that a veritable fashion arms race exists among the Rogue Trader community, and hats including anything from Tyrannid skulls and Eldar soulstones, all the way to integrated weaponry and suspensors to help carry the weight, have been seen. Current contenders for the most impressive hats include Lord Derrick Von Marsten with his self-repairing necrodermis and wraithbone tricorne with integrated force field and a hidden extensible handle to use the entire thing as a power axe, and his arch nemesis Lord Samuel Godwine, whose hat is a replica of the legendary battleship Dominus Astra, and comes with a full complement of digi-lasers for the lance batteries and a miniature bolter in place of the nova cannon, and an integrated grappling hook gun behind the ramming prow. Of course, Ork Freebooter Kaptins were quick to join in the fun, with the Ork's preference for large and loud objects leading to truly grotesque hats.
The stupid must be bashed upon the head with the Mallet of Wisdom until their heads are inflated with knowledge.
Words to live (and die) by : "I have officially Been out-rogue tradered! As always, one must always assume that no matter how grand your plan is, it's never enough!" - RogalDorn1