The difference between cynical and selfish
is that “cynical” is of or relating to the belief that human actions are motivated only or primarily by base desires or selfishness and “selfish” is holding one’s own self-interest as the standard for decision making.
The difference between self-serving and selfish
is that “self-serving” is showing interest only in oneself and “selfish” is holding one’s own self-interest as the standard for decision making.
The difference between narcissist and selfish
is that "narcissist" is one who shows extreme love and admiration for themselves and "selfish" is holding one’s own self-interest as the standard for decision making.