"The other thing I want to clear up right away is that this was MOM’s idea, not mine."
This is the ultimate thing a middle school boy who starts a diary would say, and it sets up Greg as both a kind of "every-guy" character and a typically conflicted pre-teen. His mom makes him start the diary and he wants everyone to know, but he ends up writing in it all school year. This sense of inner conflict will appear again and again throughout the book.
"The best I can figure out is that I'm somewhere around the 52nd or 53rd most popular this year."
Greg is both fixated on being popular so that he would avoid getting bullied and win the attention of all the girls, and neurotic and even dorky enough to try to calculate his exact popularity ranking, even if it's a low one. It's one of the many hilarious details in the book that Greg writes which inadvertently reveals his true nature.
"Rowley is technically my best friend, but that's definitely subject to change."
This quote sets up Greg's and Rowley's friendship, which we'll see develop, collapse, and then be rekindled over the course of the book. We know from the get-go that Greg feels conflicted about his relationship with Rowley, and doesn't really feel all that committed to him as a friend. This will become relevant later.
"Let's you and me have a talk, FRIEND."
Greg's dad only refers to Greg as "friend" when Greg is about to get in trouble. We first see this happen when Greg wakes his dad up while blasting a heavy metal CD on the stereo.
"I tried to show Rowley's dad our original plan to prove that we were really running a legitimate operation, but he didn't seem convinced."
Rowley's dad discovers Shane Snella curled up under a bed in Rowley's basement in the midst of Greg's and Rowley's failed attempt to run a haunted house. They had drawn up plans and made a big effort, and Greg trying to explain as much to Rowley's dad shows the real bummer about being a kid: you can envision a whole elaborate plan and try something ambitious, and adults just won't get it.
"It took people about five seconds to realize how 'P. Mudd' sounded when you said it out loud, and it was all over for Preston."
We really have it all in this quote. There's the juvenile humor and sense of cruelty that would lead to someone getting bullied about his name, with kids in middle school taking something as small as someone's first initial being "P" and give him a hard time for the fact that it sounds like "pee." This quote also shows us Greg's habit of looking for any way he can to justify his lack of ambition, using this joke as an example of why he would never want to be named Athlete of the Month.
"I just hope that everyone who came to see the play was as entertained as I was."
After Greg disrupts the school production of The Wizard of Oz by getting all the other boys playing trees to throw apples at Patty Farrell, which breaks her glasses and makes Mrs. Norton end the play early, all Greg can think is how happy he is that he ruined Patty Farrell's day. Greg's total lack of empathy or sense of responsibility is definitely his worst quality, and it speaks to an immaturity that will just come back to bite him later in the story.
"Because imagine if all you got for Christmas was a wool sweater."
Greg is reflecting on how his mom is always giving bad gifts to the Giving Tree, a charitable organization that gives Christmas gifts to people in need. He's going on and on about how terrible it would be to get one of the wool sweaters his mom always buys—but ironically, later in the story, he'll end up getting a wool sweater for Christmas too. It seems like karma.
"But get this: Rowley was mad at ME for what my DAD did."
This is one of those big a-ha moments, when we realize that Rowley is probably the more mature of the two friends. Greg has no idea why Rowley would be mad at him for his dad enacting punishment on Greg for destroying Manny's snowman. Rowley simply expects his friend to take some responsibility for messing up, but Greg refuses to, and it infuriates Rowley.
"That's when I decided to speak up. I told everyone I knew what happened to the Cheese. I said I was sick of it being on the blacktop and I just decided to get rid of it once and for all."
This is the first time we see Greg show that he cares about his friend Rowley, and his little fib prevents the whole school from finding out that older kids made Rowley eat the disgusting cheese that was sitting on the basketball court for ages. Greg stands up for his friend and it's a satisfying moment for the reader, since finally Greg is showing that he wants to do the right thing for a friend who's so good to him.
