*UPDATE on June 26th 2010* : steet has decided to remove this list, because this complicates the rules way too much. See the last messages posted for more info.
Thanks to Ara for the list. Keep in mind that the acronyms not on the list are under debate, and will be updated to Allowed or not allowed as needed. I recommend you refrain from using those as well.
Items listed in the colour Red or Blue are new.
Allowed:
lol/Lol
brb
bbs
np
gtg/g2g
nm
bbl
omg
btw
imo
imho
Questionable:
w00t
uber
asap
pwned/pwn
ttyl
atm (At The Moment)
Not Allowed:
cba / cbb (can't be arsed/can't be bothered)
u
r
c
4
2
8
any1/ne1
2day
2morrow
l8r
m8
ppl
h8
gr8
4nd
wtf
wth
b4
ily
143
w8
lmafo
lmao
stfu
omfg
omgwtf
roflmao
omgwtfbbq
p0rn/pr0n
n00b/noob
snafu
Acronyms not on the lists:
cus = because
zzz = bored/tired
ty = thanks/thank you
yw = you're welcome
jk = just kidding
jp = just playing
jw = just wondering
w/e = whatever
thnks/thnx = thanks
afk = away from keybored
ttfn = tata for now
ttly = totally
btw = by the way
idc = I don't care
idk = I don't know
ez = easy
zomg = misspelling of omg
yagtoh = you're going to own him
ytmnd = you're the man now, dog
ykw = you know what
yhbt = you have been trolled
wysiwyg = what you see is what you get
w/ or w/o = with or without
wrt = with regard/respect to
wuu2 = what are you up to
wubu2 = what have you been up to
wtg = way to go
tyt = take your time
tyvm = thank you very much
ttbomk = to the best of my knowledge
tmi = too much information
asap = as soon as possible
mia = missing in action
kia = killed in action
awal = absent without leave
tia = thanks in advance
tgif = thank god it's Friday
tg = that's great
sk8/sk8r/sk8er = skate/skater
scnr = sorry, could not resist
re/rehi = hello again
rofl/roflol = rolling on the floor laughing/rolling on the floor laughing out loud
rl = real life
rsn = real soon now
qwp = quit whining please
qft = quoted for truth
pov = point of view
pos = piece of ****/parent over shoulder
plmk = please let me know
paw = parents are watching
b& = banned
moar
suxxor/suxorz
kekeke/kek
lulz/Lulz
plz
cya
sthu (shut the hell up)