Sissy (derived from sister; also sissy baby, sissy boy, sissy man, sissy pants, etc.) is a pejorative term for a boy or man who does not conform to "standard male" gender stereotypes. Generally, sissy implies a lack of courage, strength, athleticism, coordination, testosterone, male libido, and stoic calm, all of which have traditionally been associated with masculinity and considered important to the male role in Western society. A man might also be considered a sissy for being interested in traditionally feminine hobbies or employment (e.g., being fond of fashion), displaying effeminate behavior (e.g. using hair products or displaying limp wrists), being unathletic, or being homosexual.
Sissy is, approximately, the male converse of tomboy (a girl with masculine traits or interests), but carries more strongly negative connotations. Research published in 2015 suggests that the terms are asymmetrical in their power to stigmatize: sissy is almost always pejorative and conveys greater severity, while tomboy rarely causes as much concern but also elicits pressure to conform to normative gender roles. Applied to an individual, these terms become a form of social control, enforcing normative gender roles and often drawing on the unfounded link of gender nonconformity with homosexuality.
History and usage
The term sissy has historically been used among schoolchildren as a "relentlessly negative" insult implying immaturity and gender or sexual deviance. It has been identified as "sexist" in guidance issued to schools in the United Kingdom and described as "just as unacceptable as racist and homophobic language." The terms gender creative, pink boy, and tomgirl  have been suggested as polite alternatives. The Japanese word bishōnen is also a polite term for a man or boy with gentle or feminine attributes.
The word sissy in its original meaning of "sister" entered American English around 1840-1850 and acquired its pejorative meaning around 1885-1890; the verb sissify appeared in 1900-1905. In comparison, the word tomboy is approximately three centuries older, dating to 1545-55.
By the 1930s, "there was no more damning insult than to be called a sissy" and the word was widely used by American football coaches and sports writers to disparage rival teams and encourage ferocious player behavior. The use of the word sissy was "ubiquitous" among delinquent American youth of the 1930s; the term was used to provoke boys to join gangs, demean boys who violated group norms, force compliance with the mandates of masculinity, and justify violence (including sexual violence) against younger and weaker children. Good students were taunted as sissies and clothing styles associated with higher social classes were demeaned as sissified. Among members of a Detroit youth gang in 1938-39, sissy was "the ultimate slur" used to tease and taunt other boys, as a rationalization for violence against rivals, and as an excuse for not observing the dictums of middle-class decorum and morality. Thus, it appears that sissy served as a multi-functional insult, which was used not only to harass the person or group at whom it was directed, but also to reinforce gender stereotypes and gender binarism, assert men's dominance over women, disparage the weak and shy as well as the homosexual and transgender, penalize behavior that varied from gender norms, encourage aggressive behavior, and critique members of higher socioeconomic strata.
The spelling variation cissy was used in British English, at least prior to the mid 1970s. In the United States, the Comedy Central television series South Park inverted its meaning in a 2014 episode titled The Cissy, which lampooned the controversy over transgender students' use of school restrooms; in the episode a restroom initially designated for use by transgender students is later re-designated as "the cissy bathroom" for use by trans-phobic cisgender students.
Term of affection toward women
Sissy (or sis) can also be a relationship nickname formed from sister, given to girls to indicate their role in the family, especially the oldest female sibling. It can also be applied to girls as a term of affection from friends who are not family members.
In gender and LGBT studies
The term sissyphobia denotes a negative cultural reaction against "sissy boys" thought prevalent in 1974. Sissyphobia has more recently been used in some queer studies; other authors in this latter area have proposed effeminiphobia, femiphobia, femmephobia, or effemimania as alternative terms.
The discourse of straight-acting produces and reproduces anti-femininity and homophobia (Clarkson. 2006). For example, feminine gay men are often labeled "fem," "bitchy," "pissy," "sissy," or "queen" (e.g., Christian, 2005; Clarkson, 2006; Payne,2007). They are perceived as if they perform like "women," spurring straight-acting gay men to have negative attitudes toward gay feminine men (Clarkson, 2006; Payne, 2007;Ward, 2000). This is called sissyphobia (Bergling, 2001). Kimmel (1996) supports that "masculinity has been (historically) defined as the flight from women and the repudiation of femininity" (p. 123). Thus, sissyphobia plays as the communication strategy for straight-acting gay men to justify and empower their masculinity. (p. 38).
Eguchi added, "I wonder how 'sissyphobia' particularly plays into the dynamic of domestic violence processes in the straight-acting and effeminate-acting male same-sex coupling pattern." (p. 53).
In sexual subcultures
In the BDSM practice of forced feminization, the male bottom undergoing cross-dressing may be called a sissy as a form of erotic humiliation, which may elicit guilt or sexual arousal, or possibly both, depending on the individual.