General Posting:
DH - Dear husband/Darling Husband, or Darn Husband,
depending on the circumstance
DW - Dear wife (there is *no* Darn Wife,
needless to say 
)
BTW - by the way
KWIM - know what I mean?
FWIW - for whatever it's worth
OP - original poster
YW - you're welcome
WB - welcome back
NVM - nevermind
RAK - random act of kindness
TY - thank you
TYVM - thank you very much
TIA - thanks in advance
HTH or H2H - happy to help
JSYK - just so you know
FYI - for your information
TFS - thanks for sharing
TMI - too much info
IMO- In my opinion.
JMHO - Just My Humble Opinion
YT - Yorkie Talk
TTFN - Ta-Ta For Now
ETA - edited to add
LMAO - laugh my ___ off
LMBO - laughing my butt off
ROTFLMAO - Rolling on the floor laughing my a _ _ off! (LMBO=laughing my butt off)
ROFL - Rolling on the floor laughing
PM - private message
DIL - Daughter in law
SIL - Son in law
MIL - Mother in law
BIL - brother in law
PPL - People
MIA-Missing in action
j/k - Just Kidding
BRB - Be Right Back
HTH - hope that helps
BYB - Back Yard Breeder
BM - Bite me
FB - Facebook
OMG - oh my God/gosh/goodness
TTYO - talk to ya later
TMTC - too many to count
AATK - asleep at the keyboard
Diseases / Health Issues
LCP - Legg Calve Perthes
LP- Luxating Patella- Slipping knee cap
LS - Liver Shunt
MVD - Microvascular Dysplasia
AAI/AAS - Atlantoaxial Instability/Atlantoaxial Subluxation
GME - Granulometous Meningioencephalomyelitis
HGE - Hemorrhagic Gastroenteritis
HE - Hepatic Encephalopathy
UTI - Urinary Tract Infection
CT - collapsed or collapsing trachea
RS - Reverse Sneeze
DM - Diabetes Mellitus
DI - Diabetes Insipidus
Medical Terms - General
Dx - diagnosis
Tx - treatment
WNL - within normal limits
NAR - not acting right
HBC - hit by car
Rx - therapy/prescription
BID - twice a day
TID - three x day
QID - four x day
HS - hour of sleep
OD/SID/QD - once a day/every day
QOD - every other day
PO - by mouth
NPO - nothing by mouth
IM - intramuscular
IV - intravenous
SQ/subq/subQ - subcutaneously
MM - mucous membranes
PTS - put to sleep
Attitude/Demeanor: BAR - bright, alert, responsive
Attitude/Demeanor: QAR - quiet, alert, responsive
Attitude/Demeanor: DEP - depressed
Medical Testing / Labs
CBC - complete blood count
BA - bile acids
BAT - bile acids test
CRT - capillary refill time
U/S - ultrasound
U/A - urinalysis
Cysto - Cystocentesis
Associations / Organizations
AAFCO - American Association of Feed Control Officials
AVMA - American Veterinary Medical Association
AAHA - American Animal Hospital Association
ACT - American College of Theriogenologists
ACVN - American College of Veterinary Nutrition
ACVS - American College of Veterinary Surgeons
AHS - American Heartworm Society
ACVIM - American College of Veterinary Internal Medicine
AKC - American Kennel Club
YTCA - Yorkshire Terrier Club of America
CKC - Canadian Kennel Club