Anime Hair: Constantly lampshaded, though he also got the front part matted down and Hobbes suggested curling the back once. Another time, he made his hair a giant swirl with Crisco, his mom made him wash it out, but there was still some that Hobbes used to style his hair like Astro Boy, which made it hair from an actual anime.
Attention Deficit... Ooh, Shiny!: He's very easily distracted, especially from things that don't interest him much in the first place (like school, homework and chores). Most often, as part of his Cloudcuckoolander nature, it's his own mind that provides the distractions — but he has been known to suddenly get distracted by external things as well.
Berserk Button: Anytime Hobbes implies that he has a crush on Susie. He also gets angry when Hobbes explains or mentions the Noodle Incident and, in one strip, asks him why he's wearing short pants.
At one point, he also throws a fussy fit when Hobbes beats him at checkers.
Heck, said "fussy fit" is the page quote for Sore Loser!
"You win? Aaugghh! You won last time! I hate it when you win! Aarrggh! Mff! Gnnk! I hate this game! I hate the whole world! Aghhh! What a stupid game! You must have cheated! You must have used some sneaky, underhanded mindmeld to make me lose! I hate you! I didn't want to play this idiotic game in the first place! I knew you'd cheat! I knew you'd win! Oh! Oh! Aarg!"
Bratty Half-Pint: Hoo boy. Calvin knows he's often a jerk, especially to his parents, but he does it anyway.
Brilliant but Lazy: He's unusually cultured in vocabulary, philosophies, very knowledgeable about dinosaurs, and has an advanced sense of irony, but since school often teaches everything he doesn't like to learn, he just doesn't bother. He could easily succeed in school if he applied himself - in one strip, he gets a good grade, but feels that it just isn't worth the effort. On the other hand, he is just impossibly bad at basic math.
More than one strip suggested that his grades at math were simply because he found the subject incomprehensibly boring.
Butt Monkey: Although it's usually justified because of his general attitude, sometimes he gets treated unfairly; in the baseball arc, he signs up because people look down on him for not participating, gets berated for accidentally catching the ball for the other team, and gets called a "quitter" when he quits the team under the pressure.
Byronic Hero: Despite being a six-year-old kid in a newspaper strip, he qualifies for this sub-type.
Calvin's stuffed tiger doll...or maybe his Not-So-Imaginary Friend. Named after Thomas Hobbes, he's usually seen through Calvin's eyes as an actual tiger while everyone else sees a doll. He's a proud tiger nonetheless and ultimately Calvin's best friend.
Cats Are Mean: Played with. Hobbes has much stronger moral integrity than Calvin, calls him out on various misdeeds, and often tries to convince him to seek happiness from virtue instead of playing pranks, but he also greatly enjoys roughhousing at Calvin's expense, getting under his skin, or freaking him out.
Characterization Marches On: In the early years, Hobbes really wasn't all that much of a snarker, and was frequently just as immature as Calvin. In later years he also became a lot more feline — not only in looks and movement, but in behavior and outlook.
The Conscience: Although he won't try too hard; Calvin's the one who'll have to suffer the consequences, after all.
Furry Reminder: We get various reminders that he is a tiger: He sleeps a lot, chases his tail and enjoys pouncing among other things.
The Gadfly: He never passes up a chance to annoy, frustrate or freak out Calvin, purely for his own amusement. Most of the fights or arguments between the two seem to ultimately be started by Hobbes pouncing, teasing or pranking Calvin in some way (though Calvin is by no means innocent and often gives as good as he gets).
Karma Houdini: He constantly beats Calvin up without being provoked (and he enjoys it) and always gets away with it.
Knight in Sour Armor: Hobbes is apparently quite cynical, but often does good deeds he doesn't expect to be rewarded for. (Ie. Trying to preach virtue to Calvin. You know, the same guy who tries to pin things on Hobbes when caught.)
Proud Warrior Race Guy: Well, replace "Warrior Race" with "Tiger". He's very proud of being a tiger, and Calvin pokes fun at him when he displays qualities more commonly associated with housecats such as lounging in the sun or being lazy.
Pintsized Powerhouse: Calvin fails to learn that no matter how big a water balloon or snowball he ambushes Susie with, it won't stop her from immediately popping up and kicking the stuffing out of him.
Tough Love: Calvin once asked his mom if he could smoke cigarettes. She gave him some his grandfather left over, surprisingly enough. He threw a huge whooping cough, causing his mom to walk over and say "I guess we learned a little lesson here."
Women Are Wiser: Inverted on a few occasions when dealing with Hobbes. She once confessed some of her fears to him when Calvin wasn't around, and on another occasion she called out for him when she and Dad were in the woods looking for him at night.
Then again, depending on how you interpret Hobbes' reality and with a little dash of Wild Mass Guessing, this could be played straight.
Abusive Parents: A mild example. While he loves his son, he enjoys feeding "facts" to Calvin, such as the origin of black and white photographs, and has often stated that he wanted a dog instead. Ok, Calvin isn't an angel, but still a harsh thing to say.
Born in the Wrong Century: Dislikes modern technology and other recent developments, like the gradual decline of people's mannners.
Bourgeois Bohemian: Dad eventually became a walking Author Tract, making speeches about commercialism and materialism and the horror of our age and the fulfillment that comes only with being miserable in the great outdoors.
Pet the Dog: Stopped working to play with Calvin until his bed time, causing Calvin to actually give him a kiss. Then he had to work into the night.
He also takes the time to read Calvin a bed time story every night.
The Scrooge: Calvin has a very frugal father. He horrifies Calvin with plans for buying used Christmas Trees, sticking it in the basement, pretending the tree is covered in lights (to save on decorations), etc.
Another gag is Calvin waking up his parents at precisely 12:01 AM to rip open his presents.
CalvinACQUITTAL ON ALL CHARGES!! COMPLETE EXONERATION!! AHA HA HA HA HA HA!! Mom:(completely unfazed by her son's megalomania) Merry Christmas to you too, dear. Dad: What's that smell? Has someone been eating tuna at this horrible hour?
It's not enough that we have to be disciplinarians, now we need to be psychologists.
Calvin's first-grade teacher. Mrs. Wormwood struggles mightily to be patient with Calvin and yearns for retirement. Watterson named her, somewhat obscurely, after a low-ranking demon in The Screwtape Letters.
Then again, she seems to give much harder questions than a first grader is expected to know. An especially egregious example (besides the insect collection) involves a word problem that requires knowledge of multiplication and algebra!
Sitcom Arch-Nemesis: Until he learned otherwise, Calvin 'sort of assumed' that his teacher slept in a coffin all summer.
Karma Houdini: Torments and beats up Calvin without provocation, and never really receives any punishment or payback. Though Calvin did appear to get the better of him when he introduced him to Hobbes, an act that confused Moe so much that he practically begged that Calvin leave him alone.
Painting the Medium: He is the only character who speaks in mixed caps instead of all caps, and his speech appears to have been written with a pencil.
For eight bucks a night, I don't put up with much.
Calvin's babysitter. She's often the only one in the neighborhood willing to babysit Calvin for his parents, provided she gets paid extra of course.
Ascended Extra: Watterson created her for just one story arc, but quickly realized having a character Calvin was actually intimidated by could provide a lot of material, so she appeared several more times.
Batman Gambit: In her final appearance in the strip, Rosalyn uses this to get Calvin to behave. She makes him want to do his homework and clean his room by offering to play Calvinball with him, and then actually wins the game when they play it, having learned about the (lack of) rules in the course of it.
Blackmail Is Such an Ugly Word: As the only babysitter in town who will agree to babysit Calvin, she's in a primo bargaining position. College tuition, y'know.
Phrase Catcher: "If you're Calvin's good side, you should be a lot smaller."
The Reveal: Calvin's mother initially thinks Calvin has turned over a new leaf, but when he leaves for school, Calvin and Hobbes are seen hiding under the bed, commenting on their success.
Shadow Archetype: Contains many qualities Calvin would like to ignore, such as helpfulness, diligence, and a crush on Susie.
Calvin's uncle, on his father's side, who lives far enough away that he hardly ever sees Calvin and his family.
Chuck Cunningham Syndrome: Essentially the reverse Rosalyn; he was intended to be a recurring character, but after the arc Watterson realized he didn't have much personality, didn't bring out anything new in Calvin, and also required some awkward writing to avoid having him call his brother and sister-in-law by their names.
There are several of these, due to Calvin's rampant imagination, including Wonga-Taa (King of Jungle) and an unnamed, enormous carnosaur known to science only as the Calvinosaur. The most common personae, however, have their own folders below.
Minimalist Cast: Stupendous Man is the only visible character in these daydreams. Other characters are alluded to (Mom Lady, Babysitter Girl, Crab Teacher), but we only see them when the POV switches back to the real world.
Paper-Thin Disguise: Subverted. Calvin thinks his hood and cape hide his identity, when they actually don't.
Guns Are Worthless: You could probably count the number of times his gun hasn't backfired on him or proven ineffective against his target on your one hand. Then again, considering Calvin's Weapon of Choice in reality is a suction dart pistol, and the aliens often represent his real life enemies, it's clear that his imaginary weapon's effectiveness is equivalent to his real weapon's.
Art Shift: Noir art, which is almost completely black with some white so you know what's going on. Watterson mentions he did it purposely to make it harder to look at, as the eye, being lazy, favors blank white spaces.
Real Life Writes the Plot: Watterson says that the main reason Tracer made so few appearances was simply because the Noir-ish art took too long to finish. If it hadn't, we might've been given more Tracer Bullet cases to enjoy.
In-universe, Calvin is first seen using the Tracer Bullet fantasy when he is covering up a bad haircut with a fedora.
''I didn't like the way this story was shaping up, so I decided to write a new ending with my .45 automatic as co-author... My friend made three profound arguments while I excused myself. I always leave when the talk gets philosophical. Just as I finished putting all the puzzle pieces together, the dame's hired goon jumped out of nowhere and practiced for his chiropractic degree."