For a gun guy the default is a loose button-down Hawaiian shirt with a pair of jeans or dress pants. The looseness gives him extra room for the lump at his waist where he carries his gun. The pattern of the Hawaiian shirt creates visual movement, and a dark color palette will further help hide the lump. This guy can easily carry outside the waistband with a strong belt supporting a holster that clips on the outside. He just needs to make sure his shirt is long enough to cover if he raises his arms or bends over. He can position his holster for appendix carry, so named because the gun is in the general vicinity of the appendix, somewhere between the hip and the navel.