omg and wtf are pretty standard internet acronyms, but WIFOM is mafia-specific so why didn't you actually define it?
WIFOM - Wine In Front Of Me
Refers to a scene in the Princess Bride where guy is given a choice of drinking the wine in front of him, or the wine in front of the other guy. The caveat is that one of the glasses is poisoned. The idea is that the hero chooses the glass in front of the other guy, since the villain is trying to poison him. However, since the villain knows that he would know that, he would put the poison in front of himself instead. However, since the hero knows that the villain knows what he knows, he might pick the one in front of him anyway, etc.
So if you see someone using WIFOM, it basically means that they're talking about what the mafia may or may not do, and what would or wouldn't be a good idea for them. If we know something would be bad for a mafia player to do, we'll be on the lookout for that kind of behavior. However, since the mafia knows this, they can get away with some of this behavior, and claim that the mafia would never do that because it gives them away, etc.
It has many application, you'll see it brought up many times over the course of the game I'm sure.