Content Warning: This article contains mention of substance abuse, suicide, rape, and sexual assault.
As the title suggests, the characters of Shameless are all unapologetically themselves, no matter how rough around the edges they may be. Helmed by the perpetually drunk Frank Gallagher, the characters all engage in their fair share of illegal activities, often with little regard for the consequences.
However, as the beloved cast of characters grows older, they mature and begin to rethink their lifestyles. Some of the younger members would rather not repeat the mistakes of their older siblings or parents. Still, they have to make a living, which often means they have to engage in sketchy business endeavors.
Ian Gallagher
Ian does some pretty questionable things over the years, like stealing Lip's identity to enlist in the army, where he steals a helicopter. He also ends up in prison for blowing up a van.
However, he draws a line when it comes to things like killing someone or using weapons, which can't be said of some of the other characters in the show. When it comes down to it, Ian would rather stay out of the limelight and live a quiet life that doesn't cost anyone else their happiness.
Kevin & Veronica
Kevin and Veronica often collaborate in their business ventures and other life choices. Their most shameless moment is probably choosing to impregnate Carol with their children. When Carol develops a short-lived crush on Kevin, he enjoys the flirtatious attention. He and Veronica also don't have a problem with scamming customers at the Alibi, especially the hipsters who move into town in the middle seasons. However, he sometimes offers discounts and drinks on the house when he's feeling friendly.
Kevin and Veronica have a few side hustles throughout the show, including an "ice-cream van", where Kevin and Lip sell drugs. Later, Kevin repaints the van to advertise his, Veronica's, and Svetlana's topless cleaning service. He parks the van in residential streets and charges money when people want him to move it. However, he shows his softer side around his children, including Ethel and Santiago. He feels terrible about the struggles they've faced and wants to improve their lives.
Lip Gallagher
Like any other Shameless character, Lip has done some things that have landed him in a lot of trouble. However, unlike others, he comes to regret his actions later - like his affair with his professor. It takes a few years of maturation for him to realize that he was irresponsible and reckless in his youth.
Lip is notorious for self-sabotaging any chance he has to make a good life for himself, but he often hurts other people in doing so. For example, he doesn't care how his actions affect Mandy and Amanda, who support him in their own ways. In the earlier seasons, he wreaks havoc in the Jackson household and enjoys it. Still, he's not the most shameless character of the series because he does change his ways, later on, beginning with his first real attempt to become sober.
Fiona Gallagher
Fiona often feels guilty when her younger siblings have to suffer for Frank and Monica's poor choices. However, sometimes it's Fiona who's responsible for hurting her siblings, like leaving cocaine where Liam can get to it as a toddler. Fiona is often the one to host these infamous Gallagher parties, not caring about waking kids - or neighbors - in the middle of the night to blast music and get drunk.
Fiona is also pretty shameless when it comes to her romantic partners. When Steve leaves, she's very quick to move on and forget all about him, even though she almost gave up her whole life in Chicago for him. She does the same with Gus, who treats her reasonably well until he discovers she's with Sean. Finally, she cheats on Mike, who is probably Fiona's best romantic partner in the show, with his brother - multiple times.
Carl Gallagher
Carl grows a lot throughout the series, but in the early seasons, he's one of the most shameless characters. He has a worrying obsession with violence, weapons, death, and rarely ever shows any kind of affection - or shame.
His actions cause Fiona increasing concern, especially when Frank congratulates him on joining the "family business". Though he gets away with selling firearms at school, Carl ends up in jail when the clueless Chuckie exposes his drug ring to the cops. Naturally, Carl is proud and excited to go to prison and become "White Boy Carl", achieving a whole new level of shamelessness.
Karen Jackson
It doesn't get much more shameless than Karen having sex with Frank - her boyfriend's father and her mother's partner - filming it, and sharing the recording with her father. She does all of this deliberately, causing anguish to everyone who cares about her, including herself. Worse still is that this leads to her father's suicide.
Assuming that Frank killed him, Karen thanks him, then urinates on her father's grave. She also takes responsibility for essentially raping Frank, after telling everyone the opposite. Later, Karen appears to show remorse for her treatment of Lip and her mom, but she always acts out of self-interest.
Steve/Jimmy Lishman
Fiona may be quick to move on from Steve, but he isn't too worried about being unfaithful to her, either. He never apologizes or even admits to Fiona about his true relationship with Estefania, which continues even while he and Fiona are together. Before he's deported, however, Steve is relentless in his advances.
He inserts himself into the Gallagher family despite Fiona's vehement requests for him to leave her alone. There's also the matter of him lying to the family about his identity and his sketchy profession, but kidnapping Frank and smuggling him into Canada tops it all. Steve doesn't show a sliver of shame, even when Fiona is distressed and the family searches for Frank all over Chicago.
Debbie Gallagher
While Steve at least feigns remorse to win back Fiona's graces, Debbie does nothing of the kind. As a young girl, she's what Frank describes as an angel sent from heaven, but she changes to become a very manipulative and shameless character.
Apart from helping her siblings throw Frank off a bridge, Debbie steals and re-sells expensive strollers from unsuspecting mothers, rapes Matty, lies to Derek about using contraception so she can get pregnant, nearly drowns a bully at the pool on purpose, tries to seduce a cancer patient's husband (then the patient herself), takes advantage of Neil, and is generally ungrateful for everything Fiona has done for her and the Gallaghers.
Mandy Milkovich
Debbie almost drowns a girl at the public pool, and some of the other characters help to throw Frank into Lake Michigan, but Mandy does the one thing that no other main character in the show ever does: intentionally attempt murder.
Mandy is one of the few partners Lip has who actually loves him, but her love often drives her to questionable actions. When she sees that Lip still cares about Karen, she runs over her with a car, very intentionally, at a high speed. Karen survives, but Mandy wishes she hadn't.
Frank Gallagher
Frank's children are only as shameless as they are because they follow his example. In fact, he encourages it, like when he congratulates Carl on joining the "family business". For Frank, shamelessness is survival, but it's also a lifestyle he's proud of.
Frank has sex with "Butterface" until she dies; masturbates on Bianca's grave; tries to sleep with his daughter Sammi so he can have her liver (then drinks through the one he does get); repeatedly takes advantage of Sheila; pays a hitman to kill Sean then sabotages Fiona's wedding to him; collects Aunt Ginger's social security checks while she's buried in the yard; becomes a "cancer concierge"; secretly inseminates Ingrid with Carl's sperm; gives Hymie drugs; pretends Carl has cancer; calls Child Protective Services on his own family; smuggles drugs from Mexico so he can get back into the U.S. ... the list goes on.