Narcissism: Frequently blame-shifts, is a serious Attention Whore, and is somewhat self-righteous.
OCD: Bluntly refuses to use a towel that was used once by someone else, wear other people's clothes, and feels the need to wash his face after being kissed. Doesn't go in the ocean because marine life pee in it.
Sociopathy: Frequently sees to it that Rowley takes the fall for his antics, plays any number of physical tricks on Rowley, and is rather selfish and narcissistic.
Companion Cube: One Christmas, Mom got him a baby doll named Alfredo which he became extremely attached to until he lost it (actually, Dad took it and hid it). Then he replaced it with a grapefruit that he took care of in the same manner for the next 3 months.
Cool Loser: Subverted. Greg wants to be seen as such by others (the reader included), but most will tell you that Greg is a dork.
Jerk with a Heart of Gold: He has his moments, notably in Cabin Fever where when Rowley anonymously snitches on Greg for accidentally vandalizing the school, he doesn't pull Rowley into it and takes the punishment by himself.
Love Redeems: In the movies. Take a look, in the 1st movie, he was a big jerk like in the books, in the 2nd and 3rd movie, he was more likable. Holly Hills was also introduced in the second movie, coincidence?
Dogged Nice Guy: Okay, so "nice guy" might be a bit of a stretch, but when you see him try so hard to win the love of Heather Hills in the 3rd film, only for her to respond with rudeness and a cold personality, it's hard not to feel a bit sorry for him.
Karma Houdini: Subverted on one occasion when his parents ground him for throwing a party while they were away.
Kick the Son of a Bitch: Does this unintentionally to Heather, whom he was trying to win over. However when Greg turned up the volume and effects, Heather's birthday party is ruined, her dress is messed up. Heather is a complete asshole to the main characters, and the destruction of her sweet 16 is fitting punishment for her behavior. You can actually cheer on Rodrick for doing this, jerk he may be.
Not So Different: In the movies to Greg. Lets make a comparison; Rodrick has a high opinion of himself, is bad with girls, an underachiever in school, and lacks talent at the one thing he thinks makes himself cool (being a musician).
Ambiguously Gay: Sometimes, Rowley's actions are a bit suspect, especially with Greg. You'd think that a 12-year old boy would realize that sharing a "Best Friends" locket (in the shape of a heart) with another 12-year old boy would be weird or realize that being a fan of a rather effeminate pop singer isn't exactly manly. It could be argued that he's just completely unaware of these things considering that he is a Cloudcuckoolander and is completely sheltered, however.
Companion Cube: The remains of his old knit blanket, which he calls "Tingy."
Enfant Terrible: Played for laughs in book 6, where he steals supplies and leaves the rest of the family for dead during a blizzard. Greg throws out the possibility that Manny was just throwing a tantrum and didn't honestly realize he was endangering anybody, but he's not 100% convinced that's the case.
Karma Houdini: He can get away with messing with Greg's stuff solely because Mom and Dad baby him.
This gets ridiculous in book 6. He gets away with the events described in the above trope. That's right, he left the family for dead during a blizzard, and didn't get punished.
Kick the Dog: He left his family for dead during a blizzard to ensure his own survival. When Manny went missing for a day, his mother, Susan, found him in his room surrounded by food, water, toys and a space heater.
The Pirates Who Don't Do Anything: Zig-Zagged. Greg's mom doesn't appear to have a job, but he mentions that she runs an article in the newspaper, and it's implied she might have been a therapist (but one for younger kids if anything) but is implied to go to school. Otherwise... she's not really doing anything.
What Does She See in Him?: One's a snarky, Jerkass, grumpy, bumbling dad who hates teenagers, heavy metal, video games and only wants to toughen up his middle child while get rid of his eldest child. The other is a former kindergarten teacher who's a gentle, caring, well-meaning Moral Guardian mother who dances to heavy metal, loves her family for the way they are, the only thing wishing for them to be is more like a family and genuinely tries to do the best for her sons (though it's often lost because of her inability to understand the fact that problems teens face can't really be solved with methods used to solve problems for kindergarteners). They're married.
Dad (Frank Heffley)
Played by: Steve Zahn
Bumbling Dad: Averted in the books, but played straight in the movies.
Asshole Victim: A girl who treats her sister, her family, children and Greg like dirt, and who even condemns a DJ who canceled just because he went out to do a good deed, ends up with a trashed sweet 16 and smothered with chocolate. It's very hard to feel sorry for how she ended up. Even her sister Holly thanked Greg for it.
Foil: To Holly. Both are beautiful blonde rich girls, and one of the Heffley brothers has a crush on each of them. The difference? Holly is a nice and sweet girl who deserves her popularity, while Heather is a complete and utter bitch.
Karma Houdini: She didn't get punished for yelling at the drama teacher, threatening to ruin her life unless she played Dorthy in the Wizard Of Oz school play. She also goes psycho on Greg when he is unable to sing in the middle of the play, and yet she doesn't get punished.
Averted. Around the end of the second movie a dove craps on her head seconds after she tells Greg that his performance was pathetic.
In the first book and the movie Greg tells Rowley in a "secret language" that Mr. Jefferson smells like woman when he was in hearing range Greg was kicked out and it's worse when you realize that with Greg smelling like a woman probaly means smelling like flowers.