From PackRat Recipe Wiki

Free For All (FFA) is a style of play in which you form friendships with other players for the expressed purpose of stealing their cards. No notes on a Smack Talk wall are honored in this style of play. Locks are used in this case to keep cards safe from other players. This is also how the rats play the game.

FFA Lite or Friendly FFA is similar but slightly different. Players will still steal without explicit permission, but will honor their friends smack (and some won't steal from their co-op friends at all).

A note on any style of play: While the game developers acknowledge that certain people have accepted one style of play over another, none of them are officially endorsed. Please be careful when adding friends, as there is no guarantee of their actual play style due to the design of the game.