So... here is the revised list so far. I haven't proofread or formatted. Let me know what you see still missing, imagining that you are brand new to TuD and brand new to forums.

+1 – agreement with the previous poster
A1C - Glycosylated Haemoglobin (lab test that shows mean blood glucose over time)
ADA - America Diabetes Association / Americans with Disabilities Act
AFAIK - As far as I know
BBT – Big Blue Test (see TuDiabetes for info)
BG or BS – blood sugar / blood glucose
BOB - Bolus on Board (used interchangeably with IOB)
BTW – by the way
CDA- Canadian Diabetes Association
CDE - Certified Diabetes Educator
CDP - Certified Pump Educator
CF - Correction factor
CGM /CGMS - continuous glucose monitor/ continuous glucose monitoring system
CHO – carbohydrate
CSII - Continuous Subcutaneous Insulin Infusion (device) - insulin pump
CWD – child/children with diabetes
D – Diabetes
DCCT - Diabetes Control and Complications Trial Digest
Dex – Dexcom CGM
DKA- diabetic ketoacidosis
DM - Diabetes Mellitus
DOC - Diabetes Online Community
DP - Dawn Phenomenon
DTC - Disability Tax Credit ( for Canadians )
DX - diagnosis
EMT - emergency medical technician
Endo - Endocrinologist
FBG - Fasting blood glucose
FS- Fingerstick
FWIW - For what it's worth
FYI - for your information
GAD - Lab test for Glutamic Acid Decarboxylase (antibodies)
GD/GDM Gestational Diabetes Mellitus
GI – Glycemic index
GL - Glycemic load
GP - General Practitioner
HTH – Hope that helps
Hypo hypoglycaemia (low blood sugar)
I:C ratio – Insulin:carbohydrate ratio
IDDM - Insulin Dependent Diabetes Mellitus
IDF – International Diabetes Federation
IDK – I don’t know
IM - Intramuscular injection
IMO/IMHO - In my (humble) opinion
IR - Insulin Resistance
IOB - Insulin on board
ISF – Insulin sensitivity factor
JDRF - Juvenile Diabetes Research Foundation
LADA - Latent Autoimmune Diabetes in Adults
LC – Low carbohydrate
LOL – Laughing out loud
MDI - Multiple Daily Injections
mg/dl - Milligrams per deciliter (blood glucose meter measurement mostly used in the US)
MM – Minimed
mmol/L - millimoles/liter (blood glucose meter measurement)
MODY - Maturity Onset Diabetes of the Young
N – NPH insulin
NDIC - National Diabetes Information Clearinghouse
NIDDK - National Institute of Diabetes and Digestive and Kidney Diseases
NIDDM - non-insulin dependent Diabetes Mellitus
NIH - National Institute of Health
NPH - neutral protamine Hagedorn - intermediate acting insulin
OMG - Oh my goodness
OP - Original Poster
OT – off topic
PcP - primary care physician
PN – Peripheral neuropathy
PP - post prandial
Pumper – PWD who uses an insulin pump
PWD - person(s) with diabetes
R – Regular insulin
RD - registered dietician
ROFL - rolling on the floor laughing
RTMS - Real Time Monitoring System (note RTMS, TGMS and CGMS all refer to the same device)
SD - standard deviation
SF – Sugar free
SMBG - Self monitoring of Blood Glucose
SWAG – Scientific wild a$$ guess
T1 - Type 1 diabetes
T1.5 – Latent Autoimmune Diabetes in Adults
T2 - Type 2 diabetes
T3 - Family or friend of a person with diabetes
TBA – To be announced
TDD – Total daily dose of insulin
TGMS - Telemetered Glucose Monitoring System
TuD - tudiabetes.org
Tx – Treatment
WDD – World Diabetes Day (November 14)
WOE – way of eating
WTF-an unexplainable high or low bs
YDMV - Your diabetes may vary
YMMV – Your mileage may vary