Milkshake Duck

Milkshake Duck is an Internet meme that describes people who gain viral popularity on social media for some positive or charming trait but are later revealed to have distasteful histories or offensive behavior. Oxford Dictionaries defined the term as "a person or character on social media that appears to be endearing at first, but is found to have an unappealing back story", but did not consider usage of the neologism to be sufficiently long-lived or widespread to warrant inclusion in their dictionaries. The term has been connected to "cancel culture", a perceived trend of call-out culture on social media resulting in celebrities being ostracized and careers abruptly derailed by publicized misconduct.
The meme is a reference to a Twitter post on 12 June 2016 by Ben Ward, an Australian cartoonist using the online handle "pixelatedboat". His Twitter joke describes a fictional Internet viral phenomenon of a "lovely duck that drinks milkshakes" and is subsequently discovered to be racist. Ward described the Twitter message as "a pretty good joke" summing up a recent trend where popularity that comes via the Internet can be quickly undone by the discovery of something troubling in a person's past. When asked in 2017, Ward was unsure what actually inspired him to make the joke, but recalled it was partially influenced by the Chewbacca Mask Lady.
In December 2017, Oxford Dictionaries announced that the phrase was a runner-up as "word of the year", losing out to "youthquake". In January 2018, Australia's "Macquarie Dictionary" named "milkshake duck" its 2017 "word of the year".
Notable instances.
The phenomenon had some notable examples prior to June 2017, in particular with Ken Bone during the 2016 United States Presidential debate, who was initially given positive exposure, until a questionable Reddit history was revealed after his appearances. 
The demonstration of the independently developed video game "The Last Night" was a highlight of Microsoft's press conference during the Electronic Entertainment Expo 2017 due to its stylish cyberpunk visuals. Then one of its creators, Tim Soret, was found to have spoken in support of the Gamergate controversy in 2014, which led to criticism of his views a day later and tarnished the game's image. Soret apologized the next day and said his views on Gamergate and other matters had since changed. The "milkshake duck" term was quickly applied to the game. Criticism over the game and the subsequent controversy over social media led to wider adoption of the term.
American rapper and singer Doja Cat was declared the Milkshake Duck of 2018 by NME. The recording artist had experienced a viral hit with her single "Mooo!," a novelty song with an absurdist lyrical theme in which she fantasizes about being a cow. Controversy ensued when it was revealed that in a 2015 tweet she had used the homophobic slur "faggot" to describe hiphop artists Tyler, the Creator and Earl Sweatshirt, members of the musical collective Odd Future. She initially defended her remarks, writing, "I called a couple people faggots when I was in high school in 2015 does this mean I don't deserve support? I’ve said faggot roughly like 15 thousand times in my life. Does saying faggot mean you hate gay people?" Her response met further backlash, including a critical tweet by "Will and Grace" actress Debra Messing, expressing disappointment in Doja for defending past ignorance and imploring her to use her fame and platform for good. Doja Cat later issued a series of apologies for her derogatory words and deleted her tweets. The controversy generated much discourse about the limits of "cancel culture".
Shortly after his webcomic "Strange Planet" began to achieve viral success in early 2019, US cartoonist Nathan W. Pyle was described as an example of the milkshake duck phenomenon when a 2017 tweet of his was revealed that expressed Pro-life views. Pyle said shortly afterward that he and his wife “have private beliefs as they pertain to our Christian faith. We believe separation of church and state is crucial to our nation flourishing”, and were supporters of the Democratic Party.
The "reverse milkshake duck".
In October 2018, some news outlets used the term "reverse milkshake duck" to describe the reversal of one's public image from problematic to positive. A mother with the Twitter username BlueStarNavyMom3 tweeted a picture of her son, associating him with the #HimToo hashtag, suggesting he was afraid to go on solo dates due to false sexual accusations. The son, Pieter Hanson, was surprised by the post and in a newly created Twitter account posted a message saying the opposite:
That was my Mom. Sometimes the people we love do things that hurt us without realizing it. Let's turn this around. I respect and #BelieveWomen. I never have and never will support #HimToo. I'm a proud Navy vet, Cat Dad and Ally. Also, Twitter, your meme game is on point.
"The Verge" writer Devon Maloney was one of the first to put a name to the reversal, saying, "In what may have been the internet's first-ever reverse milkshake-ducking, Pieter himself finally logged on a few hours later to clear his name once and for all."
"Vox"'s Aja Romano suggested the phenomenon "might actually be whatever the opposite of a Milkshake Duck is—when a viral moment starts out seeming awful but then becomes unexpectedly good." "The Guardian" said, "Hanson's story may be one of the first instances of the reversal, as the reality of his personality—a seemingly decent and inspiring young man—is a far cry from the sexist way we were introduced to him." "Slate" described it as "a viral villain outed as, despite it all, a righteous hero."
Derivatives.
A related concept to "milkshake duck" is that of the "problematic fave", describing a notable and popular person who, despite recent offensive or harmful statements or actions, manages to retain their popularity. Entrepreneur Elon Musk has been described as a "problematic fave" following his calling one of the Thai cave rescuers a "pedo guy", apparently referencing the prominence of child sex tourism and child prostitution in Thailand, in response to criticism from Vern Unsworth, a Westerner in Thailand.
"Polygon" writer Julia Alexander argued that terms like "milkshake duck" and "problematic fave" are symptoms of current cultural conflict on the Internet in which users are ready to be outraged and have the ability to search a person's public Internet history to find statements to support that. Alexander suggested that to avoid these labels, one should not worry about what statements they may have made, but whether they show awareness that they made them and that they have grown past or changed away from them.