Anyway, I was able to find and understand a few, I am sure there are others:

AM=Atode Mata (後でまた) – see you later!

CB=Chou Bimyou (超微妙) – extremely subtle

IW=Imi Wakannai (意味分かんない) – incomprehensible meaning

JK=Joshi Kousei (女子高生) – high school girls

3M=Majide Mou Muri (マジでもう無理) – extremely impossible!

3H=Hentai.Hage.Haradeteru (変態・ハゲ・腹出てる) – perverted, bald, beer belly

3K=Kimoi.Kitanai.Kusai (きもい・汚い・臭い) – disgusting, dirty, smelly

MK5=Maji Kireru 5 byoumae (マジでキレる５秒前) – on the verge of going ballistic!

MM=Maji Mukatsuku (マジムカつく) – bloody angry

DTN=Darui Tsurai Nemui (だるい・つらい・眠い) – tired, hard, sleepy

FM= Futamata (二股) – having two lovers at the same time, two-timer

HD=Hanage Deteru (鼻毛出てる) – nostril hairs are protruding out!

Apparently these acronyms are popular amongst the youngsters, especially when they are sending sms messages over their mobile phones. So if  you want to appear younger you can use those with your Japanese acquaintances. Do you know more of those?

Addition by our friend JunJun!

Those abbreviated words are generally termed ‘KY語’.

DQN= DoKyun (ドキュン) – is one of the most recent words used by youngsters. A word of contempt indicating those mens who do not have high educational background or those companies which lack common sense.

7K＝NanaKei (ナナケー) – is also a recent word meaning the low popularity of japanese IT companies among young mens. 7K is derived from the new 3K (Kiken-Kitui-Kaerenai) adding four new word:
KisokuGaKibishi (規則が厳しい) – the office regulations are very hard
KiyukaGaTorenai (休暇がとれない) – no vacation, no time off
KesyouGaNoranai (化粧がのらない) – too tired to make-up well
KekkonDekinai (結婚できない) cannot mary

hoooo this is brilliant! 7K なんだ！ I like that one very much. I guess my company is only  3K for now

Only I was amazed there are also books about those KY語, like this one: KY語辞典.