Actor Shipping: A good amount of the fandom tends to ship the pros with either each other or their celebrity partners (if they don't already have significant others), and the show often contributes in adding fuel to the fire. Val is the most common victim of this, being shipped with his Season 16 partner Zendaya ("Valdaya") and Season 19 partner Janel Parrish ("Janelskiy"). Other examples of this are Sharkaroo (Robert Herjavec and Kym Johnson, which did turn out to be Romance on the Set after all) in Season 20 and Switch-Up pairing Alemma (Alek Skarlatos/Emma Slater) in Season 21.
Alemma aside, Season 21 did a decent job in averting this by being the first season to have a married couple (Carlos and Alexa PenaVega) competing against each other, as well as featuring plenty of dances dedicated to significant others (such as Tamar's rumba in Week 4) and two pregnancy announcements (Allison in Week 4 and Nick Carter's wife Lauren Kitt in Week 8).
Thanks to a bit of flirting in their first package, Sharna and Bonner got this treatment in Season 24, with many believing the people voting for their "showmance" got them farther into the competition than they would have otherwise.
Heather Morris in Season 24. Her packages and performances showed her to be friendly and humble. However, some viewers resented her for the simple fact that she was a celebrity contestant... by way of being a professional dancer. She may well have more impressive dance creds than some of the pros on the show. In week 4 the audience comments caught on camera were "which one's the celebrity and which one's the professional", and the other pro dancers were caught commenting on how she was better than her fill-in partner. This may have been a contributing factor for her being the only person to ever be eliminated as the highest scorer.
Carrie Ann's insistence on taking off a point for having a lift in a dance that doesn't traditionally include lifts. Some fans see it as a necessary evil for her to balance out the judging panel, since otherwise Len is the only judge enforcing adherence to the traditional dances. Others see it as excessive and unnecessary, especially since she counts even a split second of feet off the ground (which is sometimes even accidental on the part of the dancers) as a lift and will often end up scoring a dance even lower than Len does because of it.
Creator's Pet: While there's no denying he's a talented dancer and choreographer, the constant shilling of Derek Hough (to the point where the judges declared that he and his professional dancer partner deserve to win before the other finalists got their last dance) turned off many fans.
The shilling, plus that he has, thus far, been given reasonable contenders while even the other "wonder triplets", Julianne Hough (his sister) and Mark Ballas (Mark's parents raised Derek and Julianne), have been handed less-than-stellar (or popular) partners.
Zigzagged, Len (the head judge) is not the biggest fan of Derek, sometimes Len's criticism has nothing to do with Derek's partner at all. Nor is he a big fan of Mark Ballas who took creative risks (just listen to him criticizing the zombie paso doble routine.)
During the Hough-less Season 22, we instead get a Network's Pet in the form of Ginger Zee, who got Val as her pro partner and, despite delivering less-than-stellar dances most of the time, receives more praise than the fanbase feels she deserves, just because she's the chief meteorologist on Good Morning America, which tends to report quite a lot on Dancing.
She also received the first perfect score, and made it to the finale, against arguably a much more talented cast. Articles were written questioning whether there was some sort of "fix."
Val himself seems to be developing into one; between seasons 19 and 24 he's won twice and been consistently given one of the best female stars of the season. The only time he missed the finals in those seasons was with Tamar Braxton, and even that was not because of her skill level (she easily could have made the finals) but because she withdrew due to medical problems.
Elimination Houdini: Marie Osmond, Master P, Michael Irvin, Cloris Leachman, Billy Ray Cyrus, Bristol Palin, Kendra Wilkinson, Hope Solo, Melissa Gilbert, Bill Engvall, Chris Soules, etc.
Season 21 avoided this to a certain degree, with all of the weakest celebs being eliminated during the front half of the competition. Still, a lot of people weren't pleased to see Alek Skarlatos, who among the remaining celebs wasn't exactly the best, in the final three just because of his personal story, much like what happened to Noah Galloway in the previous season.
Ensemble Darkhorse: Sharna Burgess, who is considered one of the better pros and even nicknamed "Lord Sharna" by a good portion of the fanbase, but hasn't scored a mirrorball yet. Troupe member Jenna Johnson could also qualify.
Germans Love David Hasselhoff: To say this show made Bindi Irwin popular in North America would be an understatement. It really is no wonder she was her season's champion.
Growing the Beard: After losing its audience share due to the overblown double night set-up and a general negative reaction to reality shows, the change in format to have only one show a week has paid off, as has getting Erin Andrews to take over the sidekick role from Brooke Burke.
In week 2 of season 20, Nastia Liukin and Derek Hough danced a rumba to "Thinking Out Loud". Season 20 was the season the dancer on the song's music video, Brittany Cherry, made her official debut in the troupe.
During Nick Carter's first dance in Season 21, his pants' button popped out, reminding him of Joey Fatone's microphone coming loose during his first dance in Season 4, which was set to the Bee Gees' "You Should Be Dancing". Guess what song Nick ended up dancing to on Famous Dances Night five weeks later?
Back in season 19, Sadie Robertson, Mark Ballas and Emma Slater performed a trio Foxtrot to "Can't Take My Eyes Off You" by Frankie Valli. Fast forward to season 23 and Ballas was absent from the pro list... but only because he was to to be the final actor to portray Valli in Jersey Boys as the play completed its historic 11-year Broadway run.
Hollywood Pudgy: Former pros Lacey Schwimmer and Cheryl Burke for a time underwent backlash because of their weight, though that obviously didn't hinder their dancing skills.
Ho Yay: Ubiquitous. Lest we not forget Mark Ballas and Val Chmerkovskiy going head to head.
The Madonna dance by Carson Kressley with the Chmerkovskiy brothers is dripping with this. There's no doubt it was intentional.
What likely started it was the season with Steve Guttenberg. One week, his partner, Anna Trebunskaya, had to take a day off. To avoid having him fall behind, her then-husband, Jonathan Roberts, filled in to help Steve. This led to them performing their all-male Tango (which Tom dubbed "The Man-go,") on the results show that week.
Then there was the (in)famous kiss between Bruno and Donny Osmond.
Bethany Mota's samba: Derek Hough and troupe member Sasha Farber's accidental(?) kiss.
Season 21 also had its fair share of homoerotic undertones, for the most part involving, oddly enough, Carlos PenaVega (who's not only married to a woman but was also competing against said woman), such as the footage of him and Val practicing hip action for Carlos' salsa with his actual partner Witney, and an entire montage dedicated to Carlos and Alek's bromance in the finale.
Team Bruno's tango had Jodie Sweetin dancing with Peta Murgatroyd and a shirtless Nyle DiMarco dancing with an also shirtless Keo Motsepe for a bit. As some people have said, that was the most Bruno thing anyone has ever seen.
Season 24's finale gave us a whole montage of Peta's partner Nick Viall and his love for Peta's fiancee Maks, including him and Maks wearing matching "I ♥ Maks" and "I ♥ Nick" shirts.
Just Here for Godzilla: Every season will have someone notable enough to be cast that will encourage viewers to tune in.
One of the most notable ones was the elimination of Sabrina Bryan in Week 6 of Season 5, which shocked and brought tears to everyone. And it happens AGAIN, in the SAME WEEK, to her in the All-Stars season, and exactly five years to the day she was eliminated the first time, no less!
Season 17 suffered a nasty chain of them starting from Christina Milian (who got the first 10 of the season that week) to Elizabeth Berkley (got a perfect score in 1 of her dances and had a 14 point lead over Bill Engvall).
Despite constantly getting judge praise, almost getting the first perfect score of the season (in the Most Memorable Year week she had a 39), and being one of the best dancers, Season 20's Willow Shields was eliminated in the seventh week, to the shock of everyone on the show and most people watching.
Season 24: Heather Morris' elimination not only came right after her pro partner Maks returned to the show after a calf muscle injury forced him to take a four-week sabbatical (Morris danced with troupe member Alan Bernsten in the meantime), but they'd got the first perfect 40 of the season that week. Many feathers were ruffled that night.
Note that in all of her performances bar Disney nightnote Ironically, this dance was Jazz — one of the styles she specialises in she had been in the top three, and was the highest scorer for both dances in the week she was eliminated (compared to Nick, who was the lowest scorer in both dances that week). In all weeks prior, either the lowest or second-lowest couple was eliminated, and the show has never seen someone with a perfect score be knocked out (outside of finals).
Even more feathers were ruffled after Simone Biles was eliminated in the semifinals, despite geting a perfect 80 from her two dances that night, a full ten points more than the other contestant up for elimination. Unfortunately, that contestant, Cubs catcher David Ross, may well have the most fan support in the history of the program.
The reaction of Hines Ward after he and Kym Johnson completed their Argentine Tango three days after Kym nearly broke her neck.
JR Martinez's rumba to "If You're Reading This". The dance was dedicated to his fellow soldiers who didn't come home from Iraq and Afghanistan. There wasn't a dry eye in the house when the dance was done.
Len Goodman's story on how he can no longer dance due to his knees...then joining in on Nastia Liukin and Derek's Viennese Waltz in his honor.
Nick Carter and Sharna Burgess' Foxtrot to "Comin' Home, Part II", dedicated to Sharna's father and grandmother, during Hometown Glory week.
Their week 8 contemporary dedicated to Nick's wife.
Bindi Irwin's contemporary to "Every Breath You Take" in Most Memorable Year Week. For that matter, the package beforehand counts as this too. There probably wasn't a dry eye in the audience after the package and dance. Turned Up to Eleven after her freestyle to "Footprints in the Sand", when Derek surprised her by having a picture of young Bindi with her father displayed prominently on the wall at the end. Bindi took one look at it and crumpled into tears in Derek's arms.
Speaking of Most Memorable Year week, Lea Thompson's contemporary to "Dance with my Father".
Most Memorable Year Week strikes again in Season 22, with Doug Flutie's tribute dance to his parents (who died literally within an hour of each other after being married for decades), set to "The Rainbow Connection".
Two weeks later, during Switch-Up Week, it was Nyle DiMarco who turned on the waterworks as he and Sharna danced a Viennese Waltz to "I Get to Love You" and scored the first 10 of the season.
Not to mention Nyle's freestyle, set to Disturbed's version of "The Sound of Silence."
Florence Henderson attended the season 23 finale to meet up with Maureen McCormick, who played her daughter on The Brady Bunch. Florence would be hospitalized the day after the finale, and would die of heart failure the day after that.
The Scrappy: Every season seems to have at least one contestant who serves as the lightning rod for audience hate.
The Woobie: As the first (and so far only) black professional dancer on the show, many fans were excited about Keo's introduction in Season 19...only for him to be immediately eliminated in week 1. As of Season 24, Keo has been the first or second eliminated in every season he's competed in (save for Season 22 with Jodie Sweetin, where he made it to week 8). Even Erin once mentioned it in a blooper from dress rehearsals: "It's the first elimination of the season, which usually means Keo's going home."