1. Rodrick is in charge: The title directly implies that Rodrick, Greg's older brother, is now in control or "rules" the situation. This could be taken literally, as Rodrick's mischievous actions are often causing trouble for Greg, or figuratively, as Rodrick's influence on Greg and their family is growing.
2. Rodrick's rules apply: The title also hints at the possibility that Rodrick has his own set of rules, which are often disruptive and chaotic. These rules could be unspoken and involve things like pranks, teasing, and generally making Greg's life miserable.
Overall, the title "Rodrick Rules" encapsulates the central theme of the book, which is the ongoing conflict between Greg and his older brother, where Rodrick's actions and influence are central to the story. It also hints at the chaotic and often hilarious situations that arise due to Rodrick's personality and behavior.