Used to describe when a piece of gossip is highly classified information and must not be passed on. Originates from "Lurpak" butter, which is notoriously hard to spread when cold. Therefore, a Code Lurpak is information that cannot be spread.
Person 1: So, can I tell Person 3 about what happened between you and that girl last night?
Person 2: No! Definitely not! That is a Code Lurpak!