Querulant
In the legal profession and courts, a querulant  (from the Latin querulus - "complaining") is a person who obsessively feels wronged, particularly about minor causes of action. In particular the term is used for those who repeatedly petition authorities or pursue legal actions based on manifestly unfounded grounds. These applications include in particular complaints about petty offenses.
Querulant behavior is to be distinguished from either the obsessive pursuit of justice regarding major injustices, or the proportionate, reasonable, pursuit of justice regarding minor grievances. According to Mullen and Lester, the life of the querulant individual becomes consumed by their personal pursuit of justice in relation to minor grievances.

Use in psychiatry
In psychiatry, the terms querulous paranoia (Kraepelin, 1904) and litigious paranoia have been used to describe a paranoid condition which manifested itself in querulant behavior. The concept had, until 2004, disappeared from the psychiatric literature; largely because it had been misused to stigmatise the behavior of people seeking the resolution of valid grievances.  It also appears in ICD-10, under its Latin name Paranoia querulans, in section F22.8, "Other persistent delusional disorders".

Frequency
According to Lester et al. querulous behavior remains common, as shown in petitions to the courts and complaints organizations. They state that "persistent complainants’ pursuit of vindication and retribution fits badly with complaints systems established to deliver reparation and compensation [and that these] complainants damaged the financial and social fabric of their own lives and frightened those dealing with their claims."

See also
Idée fixe
Monomania
Persecutory delusion
Vexatious litigation

References
External links

Blaney, Paul H.; Millon, Theodore (20 November 2008). Oxford Textbook of Psychopathology. Oxford University Press. ISBN 978-0-19-988836-8.
Lee, Kyoungmi; Kim, Hakkyun; Vohs, Kathleen D. (1 January 2011). "Stereotype Threat in the Marketplace: Consumer Anxiety and Purchase Intentions". Journal of Consumer Research. 38 (2): 343–357. CiteSeerX 10.1.1.640.678. doi:10.1086/659315. JSTOR 659315.
Vohs, Kathleen D.; Baumeister, Roy F.; Chin, Jason. "Feeling Duped: Emotional, Motivational, and Cognitive Aspects of Being Exploited by Others". CiteSeerX 10.1.1.186.4833. {{cite journal}}: Cite journal requires |journal= (help)