Since 1972-1973, license plates for automobiles in Sweden use a combination of three alphabetic letters and three digits. It started with "AAA 001" and we're presumably working our way up to "ZZZ 999", at which point we'll maybe add a digit or something.
However, some letter combinations are forbidden. Judging by the list of banned combos, the most dangerous word in the Swedish language is "kuk", a vulgar word for penis (related to the English word "cock"). You see, quite a few of them are variations of KUK, such as CUK, CYK, KUC, etc. Normally, Sweden is very liberal when it comes to language. For instance, it's perfectly alright to use the word "kuk" on national television, though excessive profanity during shows that are popular among children is frowned upon.
(Similarly, Swedish national TV can show nudity and even (obscured) intercourse, both popular in so-called "reality" shows. Though the first reality show - The Real World - was American, Sweden popularized the concept with the show Expedition: Robinson, which was Americanized as Survivor. Oh, never mind. As long as I'm in parentheses, the plate above was created with the ACME License Maker.)
Here, in the interest of public service, is the list of all banned letter combinations, replete with my translations, explanations, and speculations as to why they're forbidden. (For some of them, I have no idea. I've noted those with three question marks. Feel free to help out.) Incidentally, the list contains no combinations using the letters I, Q, V, Å, Ä, or Ö, because those letters aren't used on license plates.
APA - ape/monkey
ARG - angry
BAJ - poo
CUC - too reminiscent of KUK
CUK - too reminiscent of KUK
DUM - stupid
DYR - expensive
ETA - Euskadi Ta Askatasuna, a Basque paramilitary group
ETT - one
FAN - damn!/devil
FEG - cowardly
FEL - wrong
FEM - five
FES - farted
FET - fat
FNL - Front National de Libération du Viêt-nam du Sud = National Front for the Liberation of Southern Vietnam
FUC - too reminiscent of "fuck"
FUL - ugly
GAM - vulture
GAS
GAY
GEY - alternate spelling of GAY
GLO - stare
GOM - palate (???)
GUB - possibly banned because it's the beginning of "gubbe" = old geezer
GUC - possibly too reminiscent of KUK
GUD - God
GUK - possibly too reminiscent of KUK
HAL - slippery, possibly also banned because it's the start of "hallick" = pimp
HAN - he (???)
HAO - ???
HAR - ???
HAS - ???
HAT - hate
HER - ???
HES - hoarse (???)
HET - hot
HJO - a town in Sweden
HKH - short for "hans kungliga höghet" = his royal highness
HMO - too reminiscent of "homo"
HOM - the beginning of "homo"
HON - she (???)
HOR - fornication, adultery
HOT - threat
HRA - possibly too reminiscent of "hora" = whore
HUD - skin
HUK - probably too reminiscent of KUK, visually
HUS - house
HUT - respect for norms, maybe too similar to "hutt" = SUP
JUG - slang for breast in English, but probably banned because it's pronounced the same as "ljug" = lies
JUK - possibly too reminiscent of "jucka" = to hump, or move the pelvis to indicate sexual intercourse (it might also be too reminiscent of KUK)
JUO - ???
JUR - pronounced as "djur" = animal
KDS - Kristen demokratisk samling = Christian Democratic Gathering (an obsolete name for a political party in Sweden)
KUC - too reminiscent of KUK
KUF - Bohemian, weird guy
KUG - too reminiscent of KUK
KUK - cock!
KYK - too reminiscent of KUK
LAM - lame
LAT - lazy
LEM - limb, also penis
LOJ - apathetic
LSD - Lysergic Acid Diethylamide, acid
LUS - louse
LUZ - maybe too reminiscent of LUS
MAD
MAO - first name of Chinese Communist leader Mao Zedong
MAS - person from Dalarna in Sweden, also tax collector
MEN - injury (also the conjunction "but")
MES - wimp
MBL - Medbestämmandelagen, law that gives unions rights to negotiate with the employer
MUF - Moderata ungdomsförbundet = Moderate Youth Alliance
MUS - mouse, but also slang for vagina (the closest English equivalent would be "pussy")
MUT - prefix meaning bribe
NEJ - no
NJA - well... (yes/no combined)
NOS - nose (???)
NRP - ???
NUP - possibly too reminiscent of NYP
NYP - slang for intercourse (almost obsolete)
OND - evil
OOO - may cause associations with orgasms (personally, I'm reminded of the "O" face scene in Office Space)
ORA - sounds similar to "hora" = whore
ORM - snake
OST - cheese
OXE - ox
RAS - race, also landslide, collapse
REA - sale
ROM - fish spawn, the beverage rum, the city of Rome (take your pick - they're all dirty)
RPS - ???
RUG - ???
RUS - a state of intoxication
SAB - maybe too similar to Saab
SAC - Sveriges arbetares centralorganisation, a socialist union
SAF - Svenska arbetsgivareföreningen, an industrial organization
SAP - Socialdemokratiska arbetarepartiet = the Social Democratic Party, which has had Sweden in an iron grip for the better part of a century (its symbol is a red monkey, shown in profile, leering at the voters)
SAT - prefix associated with Satan, the Dark Lord
SEG - hard to chew, also boring
SEK - short for "svenska kronor", the Swedish currency (thus, the owner of a car with the license plate "SEK 123" could be teased for owning a cheap car. At least I think that's the reasoning.)
SEX - six, as well as sex
SJU - seven
SOP - prefix meaning "garbage"
SOS - Save Our Sools
SPY - vomit
SSU - Sveriges socialdemokratiska ungdomsförbund = Sweden's Social Democrat Youth
SUG - suck!
SUP - a drink of alcohol, snaps
SUR - angry or pissed off, also sour
SWE - short for Sweden
SYF - possibly because it's the beginning of "syfilis" = syphilis
TAJ - similar to "taja/tajja" = to masturbate
TBC - tuberculosis
TOA - short for "toalett" = toilet
TOK - a mildly crazy person, goof
TYP - type, but also slang for weird, possibly violent, guy
TOT - German for dead (Sweden is very sensitive to the plight of the German people)
TRE - three
UCK - yuck!
USH - yuck!
UFF - Föreningen u-landshjälp från folk till folk, a chain of second-hand stores that benefits developing countries
UFO - Unidentified Flying Object
UPA - ???
USA - United States of America
WAM - too reminiscent of VAM, a white supremacist group
WAR
WTC - World Trade Center (I'm betting this was banned only a few years ago...)
WWW - World Wide Web
Superblog!! performs a public service. Stay in school! Do your homework! Don't hit girls! (Unless they really fucking deserve it!)
Update Monday @ 14:20: Count Moocko chimed in with plausible explanations for TAJ and TOT. Thanks!