Here are a list of acronyms that you might find in the message boards:

AR Assistant Referee
CK Corner Kick
CRUEF Careless, Reckless or Uses Excessive Force
DFK Direct Free Kick
DOGSO Denying Obvious Goal-Scoring Opportunity (Law 12, Sending-Off Offences 4 & 5)
FAMOA Football Association Match Officials Association
FK Free Kick
FOP Field Of Play
GK Goal Kick
ITOOTR In The Opinion Of The Referee
LOAF Laws of Associated Football
OFFINABUS OFFensive, INsulting or ABUSive language/gestures
PK Penalty Kick
RC Red Card
SBO Second Bookable Offence
SCO Second Cautionable Offence
SFP Serious Foul Play (Law 12, Sending Off Offence 1)
SUB Substitution
USB Unsporting Behaviour (Law 12, Cautionable Offence 1)
VC Violent Conduct (Law 12, Sending Off Offence 2)
YC Yellow Card