a person who believes that people are only interested in themselves and are not sincere

I'm too much of a cynic to believe that he'll keep his promise. 我怀疑这世间的一切，不相信他会遵守诺言。

A cynic might say that the government has only taken this measure because it is concerned about its declining popularity. 愤世嫉俗者会说政府之所以采取这项措施仅仅是由于对其信任度下降感到担忧。