A helpless woman (Hitman Blood Money )
This one really sets the psychopaths apart from the downright mentalists. During the "New Life" level in Hitman Blood Money (memorable as the one set in Surburbia) you have three primary objectives: kill a man, retrieve some microfilm and escape. Killing the man is fine. He's a gangster and you're a contract killer. It’s the microfilm which provides the scruples, as it’s hidden inside a necklace worn by your target's wife.
In order to obtain the hidden microfilm you categorically don't have to kill the girl. You can just sedate her and take it while she's unconscious. There are some alternative options, however. Like, burn her to death with a barbeque, drown her in a swimming pool or shred her with broken glass - and extracting the jewelry from her twitching, mangled corpse. How can you sleep at night?
Above: Bad, mad and bald. Well, he is a contract killer, but whether or not he 'wipes out' this lady is really up to you...