This list is adopted from Uther Pendragon and it is what I use in my own stories. These codes are found in the subject headlines of anything I post to ASSTR and are also used in my table of contents of my website. They follow the title of the story and are placed in parenthesis. The first code used is always the sex, age and number of individuals that the story is centered around. The next code(s) are listed alphabetically and are used to describe the behaviors of the individuals within the story.

"M,m,b" are all males.
"M" is always a male 18 or older.
"m" is always a teenage male under 18.
"b" is always a young boy, up to 12. 

"F,f,g" are all females.
"F" is always a female 18 or older.
"f" is always a teenage female under 18.
"g" is always a young girl, up to 12.

The gender is then grouped together to show who is having sex with whom. 
The only exception is when the code "nosex" is used. When there is a group 
having sex with one individual, the code "~" is used. If one group is 
dominating another group then the "/" is used with those left of the 
slash dominating the person to the right of the slash.

MF        is adult heterosexual sex
ff        is teen lesbian sex
MMM~f     means three adult men having sex with a teenaged girl
MMM/f     means three adult men dominating a teenaged girl

Bot       A male robot, designed to give sexual pleasure
bot       A verison of the same, designed to look like a teenaged boy.
Fembot    A female robot, designed to give sexual pleasure.
fembot    A version of the same, designed to look like a teenaged girl.
H         A hermaphrodite adult.
h         A hermaphrodite under 18.

1st ___   First time, if place before one of the codes it means the first
          time doing the particular form of sexual activity. If by itself
          means the first time having intercourse.
alien     Sex involving someone, or something, from off Earth.
anal      Anal sex.
BBW       "Big Beautiful Women," Appreciation of fat women.
bd        means bondage (and discipline)
bear      Hairy gay male. (Grizzly Adams)
best      Bestiality, sex with animals.
bi        Bisexuality of one or more characters.
blackmail Gaining sex through threat of exposure.
breast    Abnormally large breasts
cbt       Cock and ball torture.
Celeb     The story is about a celebrity.
cheat     Married or committed people having sex outside of the 
          commitment, cheating on their partner, as distinct 
          from swinging.
coll      College-theme
creampie  is one man's ejaculate as sucked out of a woman's
          vagina and consumed by (usually another) man
cuckold   The story involves the feeling of humiliation of a man's 
          knowing that another has replaced him in his wife's bed
dream     Sexual activity during a dream, (daydream or sleep.)
ds        dominance and submission.
enem      Enemas
exhib     Exhibitionism.
fat       Involves fat people
Fdom      a dominant female
feet      Foot or shoe fetish-story
fist      Fisting, insertion of the entire hand into anus or vagina. 
furry     Animals with human characteristics.
giant     Abnormally large (tall) persons
goth      Gothic (dark) setting
hist      Has a historical theme
hs        High School-theme
humil     Humiliation
humor     Humor. The story is intended to be funny
inc       Incest.
inf       Infantilism
job       Place-of-work theme
lac       [Lactation]  Human milk
magic     Not only magic, per se, but also demons, fantasy 
          worlds, etc.
mast      Masturbation, should be _solo. 
mc        "mind-control" a big subgenre.
Mdom      a dominant male.
menstr    Sex during a woman's menstruation
nc        is non-consensual.  This is rape in law, but the style 
          may be different.
nec       [Necrophilia]  Sex with a dead person
nosex     There is no intercourse in the story.  This is a preemptive code
          in the sense that it overrides any implication of intercourse 
          by other codes used.
oral      Oral-genital contact
parody    Imitation of a style or particular story with
          the intent to amuse.
ped       [Pedophilia]  Some participants age 12 or below. 
pett      Heavy petting 
piv       [Penis in vagina]  "Straight" sex. 
preg      [Pregnancy] Either impregnation or sex with a pregnant woman.
rape      is rape.
reluc     Woman or man says no, but loves it when person is raped.
rim       Oral-anal contact.
rom       [Romantic] All sexual acts are consensual and spring from the 
          love that one of the characters feels for another.
rough     Consensually rough sex, not always sm
sad       [Sadism]  For "just" inflicting pain
safe      Safe sex 
scat      [Scatology]  Fun with feces
ScFi      Science fiction setting.
size      Overdeveloped body-parts
sm        Sadomasochism, pain for the pleasure of both.
snuff     Killing which is supposed to arouse you.
_solo     Masturbation, as in Fsolo = masturbation by an adult woman.
spank     [Spanking], mild sm.
stroke    The author intended it simply to arouse.
swing     Swinging.  Mutually consensual adultery.
tg        Trans-gender, men being changed into women (or vice 
          versa).
tort      Torture.
toys      Vibrators or other adult toys.
tragic    The story ends sadly.
tv        Transvestite:  men dressing as women.
va        Verbal abuse. [Abusive and "dirty" language]
veg       Vegetable. Sex with food. 
viol      Violence, not necessarily connected to the sex.
voy       Voyeurism, peeking.
wl        [Wedded Lust] Sex within the marital relationship.
ws        Water sports.  Pissing.
zoo       [Zoophilia]  Caring and consensual sexual relationships
          between humans and animals.