My guy would have wavy brown hair and would be dressed in a blue-white striped t-shirt, and a light aqua shirt over it (with the buttons undone).
He'd also wear jeans, and black or white sneakers. He'd wear two dogtags on his right arm.
He'd use two Desert Eagles for a primary weapon(s) (little overpowered lol) and two small katanas for a melee weapon.
While at full health, he'd be smug and annoying (though somewhat wittty) but at <50% he'd start to panic, yelping slightly whenever a special infected attacked (and using crasser language). At <10%, he'd start to whimper a lot, and scream whenever a special infected or a horde attacked him.
Some quotes:
"Ready, guys?"
"That was nothing."
"Shoot me one more time and I'll force this katana up your ass!" (When fired at repeatedly)
"Heh, I thought this was supposed to be the apocalypse, not some lousy mob fight in a mall!"
"Haha, oh [teammate], you're so cute when you're worked up." (This really applies to both genders to make his orientation ambiguous =P)
"My, my, the colours do stand out against the red" (when looking at another teammate)
"Oh please, this isn't so bad" (when other teammates are complaining about their health)
"Hey, you guys, do you wanna take a break?" (when recovering from a fight with the horde or sp. infected at 50% health)
"(teammate), do something!"
"Ooft, that is gonna hurt tomorrow"