Mad Men is filled with some deplorable characters, but few (if any) are as bad as Pete Campbell. Pete is certainly ambitious, but he gets by more through his connections and wealth than his genuine talents for business and advertising. He often resents this, which manifests itself in over-confidence.
He's also the most squirrely character on the show - unafraid to go tattling to others or to throw a hissy fit when something doesn't go his way. That said, there are moments when he is genuinely in the right - even if those moments are sometimes steeped in his pathetic whining.
Hated: Blackmailing Don
Pete mostly plays the villain throughout season one, and part of his villainous role includes blackmailing Don. Through an unfortunate set of circumstances, Pete discovers that Don isn't who he says he is.
In turn, Pete blackmails him - either Don gives him a promotion, or he goes to Bert Cooper and rats him out. It's a horribly slimy thing to do, and luckily, it doesn't turn out well for him. Don doesn't budge, and Cooper doesn't care about the truth as Don brings in too much money.
Right: Letting Bert Know About Don
That said, Pete was somewhat right in letting Bert know about Don's true identity - if for nothing else than the good of the company. In later seasons, Don almost goes to jail when the government looks into his background (and what good would SCDP be without Don?), and it costs the firm a hefty .
Also, desertion is a serious crime, and Pete was right in realizing that. If he was found out, Don could face some serious prison time, and again, SCDP would lose its most important creative. Blackmail certainly wasn't the way to go about it, but Bert should have been told all the same.
Hated: HELLS BELLS, TRUDY!
Pete is full of great one-liners, including the famous one above. But as funny as the line and Vincent Kartheiser's delivery of it is, it still showcases Pete at his most slimy and unlikable. He comes home in a huff becomes Trudy had put them on an adoption list, and he firmly tells her that they are not adopting a child.
When Trudy asks Pete to at least discuss it with her, he unleashes on her and throws a nice chicken dinner off the balcony (a particularly hilarious image). Adoption is obviously a big deal, and Pete's reluctance is understandable - but he didn't have to be so childish and authoritative about it.
Right: Hating His Office
When Pete moves to SCDP, he immediately begins whining about his crappy office. But as annoying as his whining is, he does have a point. Pete is a big deal at SCDP, and he brings in a lot of business - therefore, he has to conduct a lot of business meetings.
However, his office is small, cramped, windowless, and comes equipped with a massive beam - a beam that both obstructs views and causes particularly nasty nose bleeds. It's not the type of office that prospective clients would love, and Pete was right to something a little fancier.
Hated: Prostituting Joan
Season five's The Other Woman may show Pete at his absolute worst. Pete and Ken have dinner with a representative from Jaguar. The rep, a sleazy man named Herb, will give SCDP his business under one condition - he gets to sleep with Joan.
Before Ken can rightfully shoot him down, Pete decides that this is an agreeable offer and goes to Joan with the offer. Don is rightfully disgusted with the idea, but the other partners agree to the plan, and Joan is successfully prostituted out for business. By this point, Pete was completely irredeemable.
Right: His Feelings Of Unappreciation
Pete is a major player at SCDP, and he brings in a lot of good business. While his ego is unfathomably and annoyingly large, he is right to have it. In many ways, SCDP couldn't run or profit without Pete, his money, and the relationship he shares with his many clients.
Regardless, he is continuously looked down upon. He is given the worst office in the building, his name isn't put on the door, and no one seems to treat him with any modicum of respect - even Roger, whom Pete is somewhat correct in calling out for his general uselessness within the company.
Hated: Prostituting Trudy
Prostituting Joan wasn't the first time that Pete debased a woman to accomplish a goal. In fact, he's not even above pimping out his own wife. Pete can't let anyone else enjoy success, so when he learns that Ken is a published author, he begins writing as well.
However, it's probably not good enough to actually get published. He turns to Trudy, whose former boyfriend is in the publishing business. The insinuation is all too clear - "if you sleep with this man, my story will be published in a prestigious magazine." Pete is absolute scum.
Right: His Eye For Social Change
If nothing else, Pete is incredibly good at predicting and answering to major social change. Many of the employees at Sterling Cooper - Roger and Don among them - are stuck in the past and unwilling to look into the future. Pete rightfully points out that sales of a particular product are stronger within minority communities and wishes to exclusively to African American consumers.
Naturally, he is chastised for this decision, as advertising directly to the Black population was virtually unheard of for a white, upper-middle-class company such as this.
Hated: His Hypocrisy
Mad Men is full of hypocritical characters - particularly Don and Pete. Pete is a serial adulterer, as he has slept with numerous women while married to Trudy. He shares something in common with Don - that being "I can sleep with other women and satisfy my own needs, but you can't."
In season 7, Pete is absolutely incredulous that Trudy went out with her ex-boyfriend Charlie - this, despite them going through a divorce and despite Pete's penchant for cheating.
Right: Kennedy Beats Nixon
Further signifying Pete's eye for social change is his correct prediction that Kennedy would beat Nixon in the suitably-titled "Nixon vs. Kennedy." The episode revolves around the 1960 presidential election, and naturally, the conservative men of Sterling Cooper firmly believe that Nixon will walk away in a landslide.
But sensing a major upheaval, Pete predicts otherwise and is laughed at for his seemingly ridiculous belief. Of course, he was correct - Kennedy beat Nixon 303-219 (and won the popular vote as well). His win was partly attributed to his excellent use of television - a fact that is ironically mirrored in Sterling Cooper's unwillingness to invest heavily in TV.