Here's my list in alphabetical order! This is a work in progress. I will update this guide as much as possible!

½= Half.com
B&M = brick and mortar store
BIN=Buy It now
Btw=by the way
CB-Chargeback
DH=Darling husband, dam, dorky husband
DW=Darling Wife, dam Wife
FB= feedback
FS= Free Shipping
FVF= final value fee 
FWIW=For what its worth
FYI= For Your Information
IMO - in my opinion
Lmao=laughing my ass off
LMFHO= Laughing My F**king Head Off
Lol=laughing out loud
MIB=Mint in Box
MO=Money Order
MISB= Mint In Sealed Box
N.O.S. = New Old Stock
NARU= Not a registered user
NPS= Non-performing seller
NPB= non paying bidder
NR=No Reserve
NWT-New With Tags
NIB-New In Box
Omg=oh my god 
OOP-Out-of-Print
PO-Post Office
OP= Original Poster
OT= Off topic
PITA= pain in the @$$
PP=Paypal
PS=Power Seller
SNAD=Sold Not as Described
ST=squaretrade
The River=Amazon
TOS=Terms of Sale
UID= Unreceived Item Dispute
UPI= Unpaid Item
UPS=United Parcel Service
USPS=United States Postal Service
WAG= What a guy!
WB= Welcome Back