Common Acronyms that used in every day conversation

24/7 - 24 Hours a Day, 7 Days a Week

AA - Alcoholics Anonymous
ABC - Already Been Chewed
AC - Air Conditioning
AD - Anno Domini ("In the Year of Our Lord")
AKA - Also Known As
AM - Ante Meridiem
ASAP - As Soon As Possible
ATM - Automated Teller Machine
B&B - Bed and Breakfast
BC - Before Christ or Because
BCE - Before the Common Era
BLT - Bacon, Lettuce, Tomato
BM - Bowel Movement
BYOB - Bring Your Own Beer
CC - Credit Card
CST - Central Standard Time
CSV - Comma Separated Value
CYA - Cover Your Ass
DIY (or D.I.Y) stands for "do it yourself
D&D - Dungeons and Dragons (a game created by TSR)
EOD - End Of Day
E.g. (or e.g. / E.G.) stands for "exempli gratia" (Latin for "for example")
EST - Eastern Standard Time
ETA (not E.T.A) stands for "estimated time of arrival
ETD ("estimated time of departure")
ET - Extra Terrestrial
ETR - Early to Rise
FDR - Franklin Delano Roosevelt
FEAR - False Evidence that Appears Real
FYI - For Your Information
GC - General Contractor or Gift Certificate
GM - General Manager
GMO - Genetically Modified (usually as in "Non-GMO")
HAZ-MAT - Hazardous Material
ID - Identification
I.e. (or i.e. / I.E.) stands for "id est" (Latin for "That is (to say)
IQ - Intelligence Quotient
ISBN - International Standard Book Number
JFK - John Fitzgerald Kennedy
MC - Master of Ceremonies
MLK - Martin Luther King, Jr.
MO - Modus Operandi
MS - Manuscript
MST - Mountain Standard Time
MTG - Magic: The Gathering
MTD - Month To Date
NIB - New In the Box
NIH - Not Invented Here
NIMBY - Not In My Backyard
OJ - Orange Juice
PBJ - Peanut Butter and Jelly
PC - Politically Correct
PDA - Public Display of Affection
PHAT - Pretty Hot And Tempting
PI - Private Investigator
PIN - Personal Identification Number
PM - Post Meridiem
PMB - Personal Mail Box
PMS - Premenstrual Syndrome
POA - Power Of Attorney
POSH - Port Out, Starboard Home
PPS - Post Post Script
PR - Public Relations
PS - Post Script
PSI - Pounds Per Square Inch
PST - Pacific Standard Time
PTO - Paid Time Off
Q&A - Question and Answer
R&R - Rest and Relaxation
RBG - Red, Blue, Green
RIP - Rest in Peace
ROYGBIV - Red, Orange, Yellow, Green, Blue, Indigo, Violet
RPG - Role Playing Game
RSVP - Répondez S'il Vous Plaît (French for "Please reply")
SOB - Son of a B*tch
SOL - Sh*t Out of Luck
SOP - Standard Operating Procedure
SOS - Save Our Souls
SPF - Sun Protection Factor (how sunscreen lotion is rated)
STET - Let it Stand (an editor's mark)
TBA - To Be Announced
TBD - To Be Determined
TEAM - Together Everyone Achieves More
TEOTWAWKI - The End Of The World As We Know It
TGIF - Thank God It's Friday
TIA - Thanks In Advance
TIP - To Insure Promptness
TLC - Tender Loving Care
UFO - Unidentified Flying Object
UPC - Universal Product Code
VIP - Very Important Person
WASP - White Anglo Saxon Protestant
WOM - Word of Mouth
WTB - Want To Buy
YTD - Year To Date

Abbreviations often show up in describing educational degrees and job titles. For example:

BA - Bachelor of Arts
BS - Bachelor of Science
MA - Master of Arts
M.PHIL or MPHIL - Master of Philosophy
JD - Juris Doctor
DC - Doctor of Chiropractic
PA - Personal Assistant
MD - Managing Director
VP - Vice President
SVP - Senior Vice President
EVP - Executive Vice President
CMO - Chief Marketing Officer
CFO - Chief Financial Officer
CEO - Chief Executive Officer

Internet Chat
LOL - laugh-out-loud
ROLF - rolling on the floor laughing
ACE - a cool experience
AD - awesome dude
AFAIR - as far as I remember
AFK - away from keyboard
ANI - age not important
CUL - see you later
CWYL - chat with you later
IQ - ignorance quotient