Gender bending is a broad category of events that can happen in fan fiction, involving playing with gender. Gender-bending is usually temporary and played for laughs. It should not be conflated with transgenderism.
Opposite Gender AU
Writing an AU in which one or more characters are, and always have been, the opposite gender is an interesting way to explore the effects of gender on a storyline. Would a female Harry Potter still have the same relationship with family and friends? What if Elrond had had a son instead of Arwen?
Opposite-gender AUs are, like all AUs, required to be plausible and well-written.
Gender-Switch
In a gender-switch or gender-swap story, a magical, technological, or utterly random effect flips the genders of one or more characters, and they have to deal with experiencing life on the other side of the gender divide. Stories like this can be anywhere from stupid to funny or even thought-provoking. The webcomic "Misfile" is an example of a serious gender-switch story.
Body-Switch
Rather than switching genders, a character switches bodies with someone of the opposite gender. Probably popularized by stories like Freaky Friday, a body-switch story allows one character to literally walk in another character's shoes.
Cross-Dressing
Whether it's a disguise, an erotic activity, a form of entertainment, or just for fun, cross-dressing simply means wearing clothing typical to the other sex. Cross-dressers may attempt to pass as the other gender, or they may deliberately overplay the opposite-gender stereotype (as drag queens/kings do).
In fan fiction, cross-dressing is usually done for the purpose of disguise, and it can be funny... but woe to the fanbrat who uses feminine clothing to bash a male character, or vice versa.
Gender-Bending in the PPC
In the PPC, Laburnum/Hemlock is fond of switching genders, and may be considered either genderqueer or multiple-personality.
Flowers can have a gender that's either fixed or depends on the observer, or have no gender. Gender and Flowers is one of the many subjects of debate among PPC agents. The Kudzu can be perceived as either gender.
It's possible for badfic to gender-bend agents. This is usually when a crash dummy malfunctions or is forgotten and an agent is Sued by the opposite-gender Sue.
During the 2009 Gender Bender Crisis, many agents were genderbent and most of them were peeved about it. They were also peeved about the 2015 Body-Swap Event.
Missions Involving Gender-Bending
- "Dragon Lady" (Harry Potter). Agents Mark, Maria, Cadmar, and Miah (DF).
- Badly maintained equipment results in unwilling gender-bending for Agent Cadmar.
- "Blood Raining Night" (NSFW) (Hetalia x Inuyasha x Legend of Korra x Hellsing x Princess Mononoke x Elfen Leid), Agents Supernumerary and Ilraen-Aroline-Fothergill (DIC) with Nurse Jennifer Robinson (FicPsych)
- Jenni spends the mission disguised as a male member of the yakuza.