Tess used to be like this as well but is trying to act better now.
Alternate Universe: According to the commentary, the chapter "Another Path" was originally intended to be set in an alternate universe where Paulo had sex with Lucy during her mental breakdown in "Another Shoulder". The final version has it as a daydream of Paulo's.
The incentives "Magic Tricks," "Disaster Dominoes," and "Another Chance" are all based in alternative timelines of varying similarity to the canon one. "Disaster Dominoes" was easily the most different.
Anchored Ship: One way to see Mike and Lucy ever getting together.
Lucy in Disaster Dominoes, to a dead Mike: "Ha ha ha ha... Sandy can't have you anymore... I'm willing to join you without a doubt... without a doubt... I love you, Mike... I'll keep smiling for you..." Followed by jumping to her death. All the while, smiling and crying...
In the chapter "Return", it's revealed that Paulo now thinks of Daisy as more of a sister anyway, and doesn't mind her going out with another guy.
However, it is hinted at in "Back and Forth" that he still doesn't want to be seen as a sexual deviant in her eyes, as he immediately notices her and seems worried about her opinion of him when Tess and Lucy start some drama because of his sleeping around and being a man-whore in general.
Mike ages earlier, though this was a good thing in the end.
Cerebus Syndrome: AND HOW! That being said, the serious chapters start fairly early in the comic's run, and a lot of the change is due to the comic going from random gags to an actual interest worth pursuing as a business, with a long-ranging plot.
To demonstrate, compare this page with this page. Beware of spoilers!
Jessica and Rachel were initially your typical high school bullies with little reason for singling out Tess aside from her being an easy target. As time went on, though, hints were gradually dropped that there was a deeper reason as to why they bullied Tess specifically, a reason that was fully revealed in "Pillow Talk".
Actually, they've always had their reason, as shown on this page. At least they did as far as Rachel's backstory was concerned.
The Charmer: Used on Daisy and attempted unsuccessfully on Lucy. Both Augustus.
Chivalrous Pervert: When the well-being of Daisy or Lucy is in danger, Paulo tends to forget his perversion in favor of helping them or, at least, trying to. He also reacted this way when Sue got hurt in Confrontation.
Combat Sadomasochist: Alejandro took two of Lucy's kicks, had his teeth smashed into each other hard enough to chip one and draw blood, and was still okay enough to beat Lucy senseless before Mike came back, smashing his face into an alley floor and still not stopping him. It took Mike and Lucy together to start the example in No-Holds-Barred Beatdown. And he beat Mike before all this happened.
Comically Missing the Point: Functionally, most of the older students to Tess. Especially Jessica and Rachel, since the lot of them bullying her is a bit hypocritical at best.
Cute Bruiser/Badass Adorable: Lucy can kick a whole lot more ass than is apparent. She's also one of the shortest characters. However, while she is the strongest girl, she still isn't as strong as most of the boys.
Also, for having a not-yet-confirmed relationship long distance with Sandy, Mike was brutally beaten by Paulo and the Female Student Body for his friendship and UST with Lucy in chapter 20. Twice. Played for Laughs.
That particular gag even continued into the next 10 or so chapters. Quite a few fans considered it to be very unfunny.
Word of God finally announced his name is Augustus, but still refers to him as Final Fantasy Cat, even within the comic!
Word of God has also given a name to another character commonly referred to by a nickname, "Rapecat" for his attempted rape of Lucy or "Confrontation Cat" after the story arc he appeared in, now has the name "Alejandro".
The aforementioned history teacher is consistently referred to as Noodles by fans (and the author), since his real name isn't known.
Flanderization: David was never really that weird, he just became so over time.
And to an extent, Abbey. He started off as a polite and chivalrous character, only showing a slight dislike for the actions of Paulo and other characters. However, he has started veering into JerkAss territory, going to extreme lengths to keep ne'er do wells in detention. However, he also started to get more screen time, more friends, and more power, and he has some pretty severe mental issues.
Freudian Excuse: Fridge Logic suggests that the reason Tess refuses to get close to Paulo is due to her similar past experiences with older students. She was hurt and doesn't want Paulo to be. The memories of what she went through will keep her avoiding the idea of trying it because she can't help but think she'll just hurt him if she does. Her moments of trying to be close to Paulo may be less likely in the future than we know.
Lucy was ostracized by boys and girls at a young age. She became less cheerful and got Yashy to love, as a coping mechanism. She's not so much unwilling to open up to others as unable to at this point. There's a lot of social trauma to work through before she begins to smile even half of the time. Hence, why her pets see her differently than everyone — she opens up to them.
Paulo's fear of barking and growling came from a somewhat-traumatic childhood experience based on them. His jerk-ish habits came from a jerk teaching him how to be "cool" as a child.
Abbey acting violent or particularly angry makes him break down at realizing he's acting like his father. Justified, in that his father was a wife-beater. Also why he took Abbey, rather than Abe, as his nickname. His father went by Abe.
The chapter "Pillow Talk" delves into why Jessica is so dead-set on making Tess miserable: Tess's then-boyfriend broke the arm of Rachel's little brother. When Jess tried to find a way to get back at Roger, Tess twisted her abortive first attempt to paint Jess as a slut.
The incentive chapter "Disaster Dominoes" was even more full of it. At least in the prior example, it was just two (later one) mugger(s) completely overpowering the main cast. Disaster Dominoes mixed things up so that everyone's lives were complete shit.
Lucy's situation with Mike just gets worse in recent time after she confesses her love for him. And then Decembercementedit.
Paulo's confident and somewhat unaffected-emotionally personality has issues of confidence after Jessica and Rachel lie just to hurt Tess, is aware of how he spent most of his relationship with Jasmine playing second to most of her life, and, earlier still, him becoming the way he is now to impress Lucy after being too shy to even talk to her.
Incompatible Orientation: Paulo begins getting jealous of Rachel's friend Matt in chapter 81, thinking that she's flirting with yet another guy. The end of the chapter reveals that although Rachel did indeed attempt to woo him, Matt is gay, and has an apparent crush on Lucy's brother, Jordan.
As a small set of examples, Katie has flirted with Mike, Paulo has had flings with girl dogs (particularly Rachel), and David hits on Lucy a lot. Oh, and David may have a thing for Mike earlier and Abbey now.
Jerk Ass: Augustus and Roger, Tessa's ex-boyfriend. As well as Alejandro, often called "Rapecat"/"Confrontation Cat", who Augustus (Final Fantasy Cat) knows, with potential dark foreshadowing for the future.
Alejandro; the only thing good thing about him is that he might have a soft spot for his henchmen Toby and Augustus.
Karmic Death/Death by Irony: Possibly, Disaster Dominoes Kizuna. The death part. She murdered four known people, and drank/played in their blood. Her murdering, as well as drinking the blood of the OD'd Paulo who had any number of STDs, was not wise.
Lovable Coward: Paulo's complete inability to cope with snarling and barking. He has an excuse. For those. Thesetwo, not so much. Jasmine makes fun accordingly. The last link even has Abbey call him a coward.
Lovable Sex Maniac: Arguably Paulo. The lovable part, not the rest. Since chapter 55, he's been better.
When Daisy tells Jess to lighten up about Tess, Jess basically explodes and gives a tirade that amounts to, "You know what? You weren't there, you have no idea what I went through because of her so SHUT UP!!" Naturally, Daisy didn't take it well.
Paulo gets this too, from Jasmine. After he has broken up with her for Lucy, when Lucy is gone she walks into Daisy's study party and finds Rachel all over him. After the party, she picks him apart with a short speech.
Reformed, but Rejected: "Pillow Talk" reveals the old Tess was quite the nasty piece of work. Small wonder she's had trouble getting others to accept her...
Remember the New Guy: Let's face it, people: Suddenly introducing Sam, Lucy's brother SIXTY-THREE chapters in was a bit jarring... Which is to say nothing of Haley, Mike's sister, who was introduced five chapters after that!
Final Fantasy Cat has a scar he tries to cover up with his hair.
Kizuna has one on her left arm. She begins to explain, but then David cuts her off and we never hear how she got it. note It's been explained on the forums that she got it from a Yakuza hitman attempting to kill her after offing her parents.
Out of Focus, but Alejandro got a scar from his old girlfriend. It's one of his defining appearance details.
Debatably, Daisy used to be this to Mike. She, seemingly like David and Paulo, who said they were stalking Lucy, would pop up for no adequately explained reason constantly. Even so, she was usually not annoying about it.
Teen Genius: Daisy, to the point that she tutored Tessa, who is two years above her.
Sue, as Paulo said, is "...too smart for me. The annoying kind of smart...", suggesting she is probably one too. That gets mentioned in Confrontation, too. She is smart, but may be outclassed by Daisy. Chapter 62 has more on this.
What Lucy's bow originally was. It's not necessary anymore, but it's her bow.
Third-Option Love Interest: As Lucy and Tess struggle over their feelings for Paulo, he finally chooses... the freshman Jasmine, introduced completely out of nowhere! However, he still harbors interest in Lucy, and ultimately breaks up with Jasmine for her. Not that he counted on her moving away, of course.
Viciously deconstructed. Lucy, while occasionally sweet, is more often than not rude, condescending, and even violent! Mike, the main object of both her abusive and dependent tendencies, finally gets sick of her BS, and even though he handles the situation less than well, quite rightfully points out that his friends always make him out to be the "bad guy" despite being all but trapped in a toxic friendship since before elementary school.
True Companions: Lucy, Mike, Paulo, David, and Daisy made the original five before Tessa and Abbey showed up in high school. Shortly after most of the main cast's Sophomore year begins, Jasmine comes into the picture. She is working towards potentially being a member.
Turn Out Like His Father: Augustus (Final Fantasy Cat) beat Abbey by implying this, but then lost since he couldn't hope to be close to Daisy afterward.
Disaster Dominoes' Abbey was a less than good boyfriend...
T-Word Euphemism: After Kizuna was inelegantly booted from the comic, the forum's swear filter was used in reverse on her name, to discourage further discussion of the character. When she has to be mentioned, it's usually as K-Dog.
Trying to post her name on the actual forums gets it changed to "getting fucked in the ass". Yes, really.
The Unfair Sex: When Mike first revealed he had a longtime crush on Sandy, he was immediately accused of 'cheating' on Lucy and suffered several Amusing Injuries at the hands of 'angry feminists'. This happened again at the end of "Left Behind", with Paulo teasing Mike about — GASP! — talking to Tess and calling a 'crazy feminist SWAT team' down on him. Has since been deconstructed in that the utter Lack of Empathy Mike has gotten from his friends after rejecting Lucy's confession because he was already in a Long Distance Relationship with Sandy only seems to be hardening his heart further.
Weaksauce Weakness: Lucy's pretty tough, but reasonably deep water or the idea of trying to swim can freak her out easily. Paulo can be reduced to cowering by mean growling and most barking. Both have childhood trauma justifying it.
Wham Episode: Chapter 51, where Lucy finally works up the courage to tell Mike she loves him... only for him to reject her on account of him already having a girlfriend. Possibly WORSE is Chapter 52, where Mike finally gets sick of Lucy's awful behavior towards him, leaving her nearly broken inside. Keep in mind that nearly the entire comic had been built upon Mike's friendship with Lucy, and his willingness to look past her attitude to see who she really was. Yeah. WHAM.
"Pillow Talk" just has to be one of the wham chapters so far. First, Mike ignores Lucy on her birthday, breaking her more, which then reveals that he's been ignoring her since the debate in "Feline Filibusters". Then, The Reveal on why Jess hates Tess (see Freudian Excuse). And then Lucy's flashback to when she had her real first kiss and Mike gave her a chance to have a relationship with him. But then, she pushes away that chance due to them being twelve at the time. When it ended, Lucy then realizes that her chances with Mike now are gone. Yeah...
What If?: "Disaster Dominoes" (thankfully noncanon) asks "What if one of the characters suddenly became an Ax-Crazy mass murderer? The answer? Very unpleasent stuff happens.
Another Path asks, What if Paulo had sex with Lucy during her mental breakdown in "Another Shoulder"? Answer: Paulo and Lucy get together and the strip would end with both Lucy and Mike happy with their respective loves.
Another Chance asks, What if Abbey didn't show up in "Love My Way"? Answer: Augustus would've just kissed Daisy, and she still would be talking to him. Oh, and Abbey and Daisy would not get together.
When She Smiles: Lucy, oh so much. We, as the viewers, see a lot more smiles than other characters.
Lampshaded in the FAQ page, where for a while, the last question was "Will Mike and Lucy end up together (or something alike)?" The answer would actually blink alternately between Yes and No. Some people took it seriously, and it was eventually removed.