cynic
//ˈsɪnɪk//
Noun
cynicSingular
cynicsPlural
1
A person who believes that people are motivated purely by self-interest rather than acting for honorable or unselfish reasons.
He's such a cynic that he doesn't believe anyone does anything without expecting something in return.
2
A person who is distrustful of human sincerity or integrity and tends to be skeptical and pessimistic.
He's such a cynic that he never believes anyone's good intentions.