Middle School (Allegory)
Greg's middle school is a microcosm, a little encapsulation of the rest of the world around him. The events that occur in his school correspond to the struggles of being a pre-teen or early teenager, and therefore the middle school stands as an allegory for a certain stage of growing up. Greg's resentment for all the stupid people and jerks in his school speaks to a disaffection with people in general during an awkward phase, and his attraction to and trouble with girls speak to a complex, new way he's starting to see the world around him.
The Cheese (Symbol)
The cheese stuck to the basketball court, while a hilarious object of widespread chagrin, is a good symbol for the things that are forbidden to middle schoolers. It's a totally arbitrary object, but they all decide collectively that touching the cheese is taboo, creating complex sets of social norms around touching the cheese, or touching someone who has touched the cheese. There are a lot of weird rules in this world, and never touching the cheese is one of them.
Throwing Things (Motif)
Guys in this book throw stuff, and they throw stuff a lot. Greg's dad throws things at Greg whenever he gets frustrated with someone Greg did. Greg seems to have picked up on the habit. He throws apples at Patty Farrell during the school play and throws a ball at Rowley as Rowley is speeding downhill on his Big Wheel tricycle. Throwing stuff is an immature act, and it's a good indication of the childlike impulses that kids and adults alike are susceptible to.
The Yearbook (Symbol)
For Greg, the Class Favorites section in the yearbook is a clear symbol of social standing. If you can get nominated for one of the Class Favorites categories in the yearbook, then classmates obviously know who you are and like you. Therefore Greg, who is fixated on his social standing, becomes fixated on earning a Class Favorites designation too. On the other hand, when Greg reads through his big brother Rodrick's yearbook, we see the section as an opportunity for someone to project their own gripes with the world onto specific people via Rodrick's scrawling all over people's photos.
Christmas (Allegory)
In a lot of fiction, Christmas represents everything from family, to the kindness of strangers, to the power of community. But Diary of a Wimpy Kid takes a similar approach as the 1983 film A Christmas Story and uses the holiday as an allegory for the pains of growing up. In this book, Christmas is portrayed as the day when everyone is getting better gifts than you and your mom accidentally gives away the video game she bought for you to charity. In this particular allegory, Greg sees Christmas not as a time for joy, but as another opportunity to be bored and a little resentful. He can't even pretend to be excited about the weight set his dad got him.
The Giant Snowball (Symbol)
The giant snowball that Greg and Rowley make together is a metaphor for their friendship. They work hard to do the fun stuff, but Greg takes no responsibility when something goes wrong, such as when Greg's dad breaks up the snowball because Greg destroyed Manny's snowman. Rowley, as he so often does in the friendship, ends up hurt.
Greg recounts that, one year, his uncle got him a Barbie doll for Christmas. It sparked tension between Greg's parents, since Greg playing with the doll was a metaphor for his ease operating outside his typical male gender role. Greg's father's disapproval shows his discomfort with his son not fitting in the conventional mold of budding masculinity.
The Robot (Symbol)
In independent study, Greg and his classmates are tasked with brainstorming ideas about what a robot they would build would do. It becomes a comical metaphor for the differences between boys and girls in middle school, as the girls want to give it the ability to do makeup and give them dating advice, while the boys spend their time making a list of words that it shouldn't say that is comprised of all the bad words they can think up.
Wrestling (Symbol)
Wrestling, and everyone's success at it in gym class, becomes a metaphor for adolescence. The ones who are better at wrestling are also the ones who have already hit puberty, and therefore seem more dominant in middle school. Greg, on the other hand, is a puny kid who hasn't hit his growth spurt yet, and his frustration in wrestling mirrors his other frustrations about popularity and the comic strip, which often boil down to an anxiety about being just another unremarkable kid.
Hot Chocolate (Symbol)
The hot chocolate is served to Safety Patrol members every morning to help them warm up before standing outside in the cold helping people, and serves as a metaphor for the perks of doing something good for other people. Greg is ultimately denied hot chocolate after the debacle where he lets Rowley get in trouble, and he responds to this like he responds to most things being taken away from him: with a sense of entitlement yet no sense of responsibility.
