All you gotta do is sneak up on him from behind and take him out with some basic CQC. Failing that use your Mark II pistol on the bastard and he'll be sleeping like a puppy. If all of that fails, just hand him a cigarette and let the addiction begin. From then onwards you can charge him exorbitant prices for your ciggies and make a huge profit. Continue doing this until he dies of cancer. However, if you're not careful you could end up getting infected:



So don't commit bestiality or anything.

Hope that helped.