While I'm sure being rough and gruff is very natural to him, it's probably also an image he's built over the years

There's a mention of this idea in the artbook, how he keeps his collar open for bravado. And all the little things in his attire that conveys of what he does/can do.

+ How he would casually roll up his sleeves, sets his jaw, and make his voice much more gravelly (than it already is.)

ah just the whole kcd clone stuff