AMC’s hit television show “Mad Men,” which returns Sunday at 9 p.m. EDT, has garnered praise for its enviable costumes and sleek cinematography, but its best quality is its ability to consistently shock viewers.

With only one day left before the long-awaited sixth-season premiere, here is our countdown of the most shocking “Mad Men” moments from past seasons.

5. Betty Draper Proves She’s Nobody To Mess With

Betty Draper might look and act like Grace Kelly when she’s at the stables or entertaining her husband Don Draper’s guests, but, in the last scene of the ninth episode of the first season of “Mad Men,” she proved she wasn’t at all worried about etiquette where her children were concerned. After learning her next-door neighbor had threatened Bobby and Sally when their dog attacked one of his beloved pigeons, Betty uncharacteristically vented her frustrations with the aid of a BB gun, making for one of the most shocking ending scenes of the series.

4. Joan’s Fiancé Rapes Her In Don’s Office

As loyal Joan Harris supporters, we all wanted to like Joan’s surgeon fiance when he was first introduced, but that dream was all but shattered when he paid her a visit at the office, and ended up raping her on the floor of Don’s office.

3. Lois Sadler Runs Over The Visiting British Boss With A John Deere Riding Mower

One of the show’s most gruesome moments started innocently enough, with some friendly riding-mower racing around the halls of Sterling Cooper at Joan’s going-away party. Unfortunately, the party went dangerously awry when secretary Lois Sadler tried her hand at driving the mini John Deere in the office, and accidentally ran over the foot of the company’s new top executive, Guy Mackendrick. Joan once again came to the rescue, bandaging up Mackendrick’s foot, and saving his life. All in a day’s work.

2. Betty Confronts Don About His Past

Don’s secret identity was practically a forgotten issue during the fifth season of “Mad Men,” thanks largely to the understanding of Don’s new wife, Megan Draper, but it was an ongoing subplot the first few seasons. Don’s struggle to compartmentalize his shady past finally came to a head when his then-wife Betty discovered the key to his desk, where he had hidden documents about his past and his stolen identity. Although we all knew it was coming somewhere down the line, the ensuing scene between Don and Betty was one of the season’s most dramatic turning points.

1. Joan’s Jaguar Deal

Joan’s decision to sleep with an executive at Jaguar to secure a deal for Sterling Cooper Draper Price in the fifth-season episode, “The Other Woman,” was one of the most divisive and shocking moments in the series’ history. Joan’s character, who the New Yorker's Emily Nussbaum has referred to as “the heart of the series,” appeared virtually unable to do any wrong. Even her choice to sleep with a slimy client in exchange for a stake in the company didn’t seem to turn viewers against her, proving how popular of a character she truly is. But the episode did give audiences a lot of pause -- and heartache for Joan, who wondered whether she had perhaps made an irreparable decision.