Peter says that Meg wasn't invited to his birthday party, and yet she appears when Peter gets his cake.
In "THE QUAHOG INFORMANT" newspaper, there is an article with the title: "LOIS GRIFFIN: Top ranked fighter in Quahog" but below, there is a smaller title that goes: "Quahog Informant to start printing news instead of just horizontal lines".
When Peter receives a globe he asks "what planet is this?" Joe says its not a planet, making it minutely possible that he was disregarding that Earth is a planet. It is very probable that it is an example of Peter's stupidity in believing the globe itself was a planet.