lol/lolz = laugh out loud
1337 = see leet
rofl/
rotfl = rolling on the floor laughing
stfu = shut the f*ck up
stmfhub = shut the motherf*cking h*ll up bi*ch
g2g/gtg = got to go
omg = oh my god
wtf? = what the f*ck
wtfwt = what the f*ck was that?
meh = tch
wth = what the heck/what the h*ll
fps = frames per second/ first person shooter
zomg = over used version of omg
haha = haha
gth = go to h*ll
lmao = laughing my a*s off
lmfao = laughing
my f*cking a*s off
hacker = someone who cheats
haxer = hacker
u = you
ur = your
4 = for
2 = to
noob = a beginner or someone who is not good
nub = noob
kick = remove
ban = permanently remove
lemme = let me
dunno = dont know
sometin = something
p*
ssy = sex
... = ok, i dont really care
g4u = good for you
ferst = first
CS = Good first person shooter
These all i can think of on the top of my head,
The 11yr old CS playa