Pale with long, dark hair wearing a partially-unbuttoned black dress shirt and matching black pants and a black trenchcoat.
Apathetic about almost everything ("Hey, uh, it looks like Dave's being mauled by the zomb- oh, never mind, he's dead now,"), probably filled with hate for the other survivors, only talking with them freely to make some sarcastic comment about how much they all suck. Also, paranoid and sociopathic, though quite calm ("Hey, I blew Steve's brains out. I think he could have possibly been infected. He had a cut and at one point was close to a zombie. You can never be too careful. Is that a bite mark on you? Ah well, let's just assume it is,").
Essentially, I'd be the creepy one that everyone tries to avoid.
I'd use an SMG and something with a big blade. Avoiding injuring others wouldn't be my main focus. Although it would be useful to have distractions/bait/shields friends for as long as possible.