In this thread, Dead Badger uses the term t’internet, which I thought only I used. Anyone else have any unusual abbreviations?
When I was a teen, my father and I were both fond of the mysteries of Carter Dickson (AKA John Dickson Carr). One of Dickson’s main characters is a detective named Sir Henry Merrivale, who attributes misfortune to “the blinkin’ awful cussedness of things in general.” My dad and I used this phrase so often that finally I abbreviated it to TBACOTIG, pronounced “tobacco-tig.” It became a family catchphrase.
IPOIO = Inherent Perversity Of Inanimate Objects.
That “force” which causes, for example, the dropped slice of toast to fall butter side down.
When I was in grad school and loaned notes to someone, I had to provide a full page crib sheet for the abbreviations. A lot of them are borrowed from Latin, which I studied in high school; from medical abbrs. (I worked in a LTC facility PT while in grad school 
) – plus my various permutations and adaptations of traditional symbols (a colon with a circle around it means “in that” or “such that”). Similarly, from “X” for Christ came X- for Christian, as well as and X-ty for Christianity (I was studying religion), etc.
A wacky system, but it got to the point where I could get down really detailed notes on a complicated lecture.
I continue to pick up new ones – s/b is “should be” in the publishing biz, and I’ve continue to adapt new ones for me own needs – like the idioscyncratic w/b, for “would be,” used when I’m providing feedback to trainees.
Only used in emails and instant/text messages:
s’ before a word = short for it’s or that’s: s’ok, s’why
dl = download
w/ = with
b/c = because
Couldn’t tell you where I got them from or why I continue to use them, considering I end up having to explain them to people.
Aside from those, there are many that I’ve picked up in places like, well, here, that most any SDMB regular would know, but that require explanation to others, like:
AFAIK
IIRC
A common one around Biker circles:
DILLIGAF
Does It Look like I Give A F**k
NFG = no fucking good
As a soldier’s wife, I can tell you that the source expert for “abbreviations” is the US military. Oy. It’s like talking in a foreign language. One that’s crossed over into my lexicon is POC (point of contact).
In my job as an insurance adjuster, we have our own version of shorthand. CV = claimant vehicle, LM/VM = left message on voice mail. We’ve even borrowed some from the medical industry such as ROM (range of motion), sx (surgery), dx (diagnosis), fx (fracture).
Usually shouted out after someone’s gone FIGJAM - F**k I’m Good, Just Ask Me.
I love abbreviations, they make my work so much easier. Typing when you’re on the phone with a customer necessitates them so much sometimes.
“Cust called to canx d/up svc as has DSL conn 15/8. Canx effective 20/8. Cust also adv cci on DSL. 4 lights on modem, showing in users online. Check dvc mgr, modem install ok. Pwr cycle modem, reboot WinXP. USB on, status & ADSL flashing. Spoke to DSL POC, suggest full iso o/night call back for further troubleshooting tomorrow am”
Working in financial services was better, though. There were even less words that made sense in the average sentence.
“Cust call re: LPF. At 30 day merc. A/c holder present. Adv broke P2P. New P2P, disco & poss merc act if FTK.”
From an old girlfriend, NIJI as a mariginal notation while reading a textbook. Means “Not Important, Just Interesting.”
I believe this crops up in a Peter Kay standup routine - although I’m not saying this is necessarily from where either of you acquired the term!
A semi-common unofficial abbreviation is lx for linguistics. I promptly generalized this to lxc for linguistic, lxist for linguist, and trx for translation/translate.
cc for copy, -> for move, rmv for remove. I have a bunch of AutoCAD commands that I apply to other programs and computers in general.
I like it! 
b4 = before
I picked up “c bar” (the letter c with a short line or bar drawn over it) for “with” - I picked that up from the medical folks.
We take POC further and get good and redundant on it, forming SPOC - Single Point Of Contact. I want to find the person that came up with it, give them a good smack and say “Duh, Becky! A point is already single!”
pw should be obvious as password
We’ve got abbreviations for our environments. Dev is painfully obvious for development, but SIT and UAT are probably not obvious. SIT is Systems Integration Testing - making sure something plays nice and doesn’t crash other applications or start putting out garbage. UAT is User Acceptance Testing - it’s handed over to beta testers who try very hard to break the thing. Usually, they don’t need to try very hard.
SEP - Somebody Else’s Problem.
From Hitchhiker’s Guide to the Galaxy.
My old roomate had a cousin who would always sign his letters, postcards, e-mails with -AMF
His initials were B.G. so we never knew what it meant.
When we finally remembered to ask him he said rather non-chalantly
“Oh, that means Adios’ Muther-fucker”