This guy really wanted you to know how tough and experienced he was. Everything he wore was scratched and frayed at the ends from use, but still intact and completely functional. His dull orange pants were just loose enough to tuck into the tops of his combat boots, and dusted with sand despite the pouring rain outside. Metal armor plates protected his thighs, letting you know he was the kind of guy never completely comfortable without armor, and I guess also that he really valued his thighs.
His faded maroon shirt didn't match his pants, because hardened, cynical soldiers don't worry if their clothes clash. Don't worry, you couldn't see much of it beneath the empty bandoliers and the leather jacket. Thick leather, of course. A man with his past might face a knife in the back or being thrown against a car at any moment. Same with the black gloves. You never know when you'll have to settle things with your fists.
Shoulder guards attached to the jacket? Of course. The ancient scarf around his neck was a good touch, no doubt hiding ugly scars from a dramatic combat while reminding him of a woman who died in his arms. Mysterious pouches on his belt and bulges in his jacket assured you he was armed, and you could take it for granted he had a knife in his boot. Streaks of grey at his temples marked not-quite-black hair. You know, because he was old enough to have seen decades of combat but young enough to be strong. Finally, a couple of patches on his jacket had faded into unidentified landscapes and illegible logos, letting you cleverly figure out that he'd been everywhere and seen everything, which always resulted in shooting people.
The first words out of his mouth would include a reference to his days as a mech pilot, so you'd know he had the skills to battle against the teenage girls with direct nervous interfaces who normally piloted mechs.