DH or OH - Darling Husband/Other Half
DW - Darling Wife
DD - Darling Daughter (DD1 if she's the first child DD2 if she's the second etc)
DS - Darling Son (DD1/DD2 etc)
MIL/FIL - Mother/Father in Law
HIWTH - Hate It When That Happens.
OT - Off Topic
BRB - Be Right Back
BTW - By The Way
HTH - Hope This Helps
IMO - In My Opinion
IMHO - In My Humble Opinion
LOL - Laugh Out Loud
PMSL - Peeing Myself Laughing
ROFL - Rolling On the Floor Laughing
IYSWIM - If You See What I Mean
IYKWIM - If You Know What I Mean
AFAIK - As Far As I Know
FWIW - For What Its Worth
FYI - For Your Information
FAQ - Frequently Asked Questions
OMG - Oh My God
IOW - In Other Words
TIA -Thanks In Advance
TTYL - Talk To You Later
WTG - Way to Go
LMAO - Laugh My ar** off
Showing/Working -
FT - Field Trial
SH - Show
JW - Junior Warrent.
BIS - Best In Show
BOB - Best Of Breed
IR CH - Irish Champion
AM CH - American Champion
(etc etc).
And for the mum and dad of a dog -
Sire - Father
Dam - Mother
I'm sure I missed quite a few but that should keep you going for now.
HTH!