This is easiest to get with Kreia and a light-side character. When talking to her always pick altruistic, self-sacrificing dialogue options and reject any teachings she tries to give you. If you don't mind character inconsistency you can also remove Atton from your party and kill a couple people on Telos: the resident of one the apartments you can break into and the receptionist for the Exchange. Kreia will lose influence both times (if Atton is there he will usually prevent this from happening with his own reaction). Doing this, I was able to get the achievement just after leaving Telos and before setting foot on any of the other worlds. If you avoid the dark-side options you should be able to get this by rejecting her advice on helping others shortly after landing on Nar Shadaa and looting one of the corpses just outside the ship on Korriban.