nudnik       
noun [ C ] US informal uk/ˈnʊd.nɪk/ us/ˈnʊd.nɪk/
 无聊的人,令人厌烦的人,爱抱怨的人
an annoying or boring person, especially someone who is always criticizing or complaining
  He earned himself the reputation of being a nudnik and a pedant. 人们都说他爱抱怨,是个书呆子。 
 What makes him such a nudnik, such a pest? 他为什么这么爱抱怨,这么令人讨厌? 
 - More examples
 - Melvin, you are such a nudnik!
 - He is painted as a nudnik simply because he's into golf and finance.
 - He plays a grandiose, macho nudnik with a raging ego and a hair-raising sense of grievance.