These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
TJ. He is always smiling whenever we see him, he's shown to be charismatic (Talking Luann's family into letting him move in with Brad and in their house when he accidentally lit it on fire, talking Brad's dad into okaying a car trip), and has been shown to concoct sometimes rude schemes to get money. However; his parents were never mentioned, and a 2008 strip very heavily implies that he suffers from Parental Abandonment. It's easy to interpret that he's a rare male example of a Stepford Smiler who has to resort to scams or unethical business practices to get by.
Anvilicious: Is it ever. A guy smoking marijuana isn't merely a druggie; he's a horrible, semi-abusive jerk to who tries to force his girlfriend (Bernice) to hide it for him. Also, Brad's inspired by 9/11 to become a firefighter and hero.
Delta is sort of an in-universe example. And her friends (including Luann) find it annoying.
Pretty much any arc that focuses on why Luann should choose Gunther as a boyfriend because he's nice and her mother likes him sooner or later deals out anvils about the evils of wanting a boyfriend based on infatuation/attraction.
Creator's Pet: Mr Fogarty, Luann's teacher. Greg Evans dedicated a full 3 weeks of story to him announcing his retirement (from a job he hates and is terrible at). And within the strips were "flashbacks" showing bits from past stories, emphasizing exactly how one-note he is. And every day a note reminded readers to follow a link to see even more of these past stories. It's doubtful anyone except Evans himself cared much about Fogarty leaving, certainly not enough to go skimming through old storylines just to see numerous examples of him being ignored and disrespected by the students. The "shilled by other characters" part comes into play when the students (Tiffany included) throw him a surprise retirement party, even though the idea of them showing him attention or gratitude goes against 25 years of canon.
Fogarty was actually the lead character of the comic Greg Evans drew for several years before Luann, so that's an entirely reasonable interpretation of the long goodbye.
Designated Villain: Ever since Quill was introduced, Tiffany shifted from merely the shallow Veronica to Luann's Betty to an outright antagonist. Her behavior hasn't changed, but the other characters' reactions to it have.
Hilarious in Hindsight: The arc where Luann runs in Clay Aiken and mistakes a note from him to mean he's in love with her is most ironic after the real life Aiken came out as gay.