Possibly his Crowning Moment of Jerkassery is in "Cartmanland", where he spends a huge inheritance on an amusement park, refuses to open it to the public, then runs TV advertisements telling everyone that they can't come.
Cartman examples could fill several pages, but the episode "AWESOME-O" really stands out. Butters generally treats Cartman at least better than Stan and Kyle (though he has admitted to not liking him much) and has never actively done anything to hurt him, or anybody. For no reason other than having material to humiliate Butters with (because he seems to get a kick out of taking advantage of Butters' naiveté), Cartman pretends to be Butters' new robot friend to find out his secrets. He doesn't feel guilty about it at any point either. That particular scheme however, backfired in several ways.
And, of course, the infamous "Scott Tenorman Must Die" episode, where Cartman was constantly humiliated by the titular teenage boy, and plots to take revenge. After failing several times, Cartman puts an Evil Plan into place, which culminates in the deaths of Scott's parents, whose corpses Cartman hacks up and bakes into chili. The next day, at a chili cook-off, Cartman feeds said chili to Scott. To add insult to injury, after Cartman reveals his plot and Scott breaks down crying, horrified that he has eaten his parents, his favorite band enters and ridicules him, calling him a crybaby and uncool before exiting stage left. To top it all off, Cartman licks the tears off of the boy's face as the crowd looks on in horror.
Stan's dad Randy was Flanderized into one as the seasons passed, devolving into a spoilt, irrational Manchild who often disregards his son to erupt into chaos over everything.
Stan's older sister Shelley, who is oftentimes temperamental, unstable and vicious, and bullied Stan to ridiculous levels in the earlier seasons.
Kyle's dad Gerald can be one. Being a lawyer has given him several other opportunities to choose the side that pays better over his own son, and he's been a jerk in other ways on occasion (like in "Smug Alert"). Taken up to eleven in Season 20 when he decides to start brutally trolling women and girls (some of them are cancer survivors, and one of them is Driven to Suicide as a direct result of his trolling) For the Evulz.
Kyle's mom Sheila as well. Her overzealous attempts to make a "safer environment" for the town's kids involving starting a war with Canada and trying to kill Terrance and Phillip in cold blood. She can also be rather overbearing to her son at times, to the point where he is shown to be outright terrified of her.
Kenny's dad Stuart is a bitter drunk who gets into drunken fights with his older son. He's also yelled at his daughter and Kenny when they've done nothing wrong at least once each on-screen.
Butters' grandma, as she bullies Butters for her amusement. This was deliberate, setting the message that people you might never suspect might be bullies — and the elderly are not exempt from being petty and cruel.
Clyde's mom Betsy emotionally abuses Clyde and humiliates him in front of his friends.
Bridon's father is a pretentious, unlikable asshole who physically assaults people over any slights.
Scott Malkinsons' father Clark is lazy, short-tempered, and belittles his son.
Lizzy, a rude and foul-mouthed female 4th grader. She is a bully who derives amusement from trash-talking the boys with slurs.
Veronica Crabtree, the former school bus driver, is unfriendly and always shouting at the kids.
Herbert Garrison, the boys' homeroom teacher, is a short-tempered, foul-mouthed, power-hungry teacher who treats his students with very little respect and rarely gets his head out of his ass to save them in the face of legitimate danger. Though since his second change in Season 12, this has been toned down somewhat. He returns to this role by Season 20, where he becomes the the President of the United States, with the sole purpose of abusing his power up to eleven in the most criminal ways possible, with rape and terrorism being his worst offenses.
Caitlyn Jenner, a male-to-female transgender former Olympic swimmer. She cheerfully joins Mr. Garrison in openly bullying others while campaigning for presidency, and regularly runs over people when driving her car.
PC Principal, a politically correct frat boy who takes over as principal for South Park Elementary in Season 19. He's very violent and threatens anyone that disagrees with him with several weeks' detention. His jerkish tendencies are toned down in Season 20 however.
Mayor McDaniels, the corrupt mayor of South Park, considers everyone in town a bunch of hillbillies and isn't above trying to convince Barbrady to shoot kids, (granted, she thought they were ISIS and the other adults were also trying to convince Barbrady to shoot).
Saddam Hussein is (somehow) worse than Cartman. He's very abusive in his relationship with Satan, and thinks he's higher than everyone else. He also once took the power of Canada as a tyrannical Prime Minister, forcing the Broflovski family to almost lose Ike, and later kills Kenny for no reason than to prove how evil he is.
Even Stan and Kyle themselves can be this at times, particularly in the earlier seasons. Season 6 has shown them to be just as manipulative and dismissive towards Butters as Cartman.
