In the past year, I've become acquainted with a term which I predominantly hear associated with female characters in science fiction and fantasy TV, films and books. The term, "Mary Sue", (with it's male equivalents, "Marty Stu", "Gary Sue", or "Larry Stu"), is used to identify fictional characters who posses traits that make them "too good to be true". They supposedly have some combination of abilities and talents which render them essentially "flawless". The proposed purpose of the term is to identify unrealistic, unbelievable characters who lack depth and detail in terms of offering any internal conflict or flaw which may drive narrative interest.
On the surface, this terminology would seem applicable to either gender equally, but in practice, I have observed a very definite bias in terms of how the term is used and against which characters. With very little variation, it is almost exclusively used against females. Even the fact that there are multiple variants of the male version tells me that its use in that context is irregular and significantly less frequent. The fact that there only seems to be a single female variant tells me that its purpose is much more aligned with some deeper sexist intent.
In recent years, there has been a marked shift within the realm of fiction towards a more inclusive, diverse narrative, with the use of competent, capable female lead characters becoming more and more prominent. In contrast with this, there has been a corresponding backlash from the male audience. A kind of "toxic" fandom has evolved within this breach whereby those who feel threatened in some way by this shift, pick out these characters and, invariably, tag them with the epithet, "Mary Sue". Recent examples include Rey in Star Wars and Michael Burnham in Star Trek Discovery, with both characters being on the forefront of so-called "fan" revolts whereby orchestrated campaigns have taken place to sabotage ratings systems with negative reviews and comments.
The use of the term seems to be intended to undermine any attempt to portray a female lead in any kind of heroic context. Any indication of significant competence and ability will trigger the use of the term. Yet male heroic characters seem to be immune to the accusation and are rarely, if ever, included in such attacks. This audience faction seems determined to retain limitations on female characters to such roles as the "damsel in distress", someone to be "saved" by the male heroic character. Attempts to modify this trope and introduce variant dynamics are seen as insincere manipulations by a "liberal" elite to introduce concepts of "social justice" as a means to violate the sanctity of male superiority and control.
I've seen it used in this context so frequently that the term has become something of a trigger word, like "libtard" or "snowflake", for that particular brand of retrograde, reactive mentality which balks at any and all attempts to think in progressive terms or address any kind of imbalance in the social sphere as it applies to gender roles and characterizations. Scratch the surface of any male tossing the term "Marry Sue" into a critique and I guarantee you'll find someone struggling with insecurities and usually lacking social tact when dealing with members of the opposite sex.