The Google search for "Walking Dead Say Uncle" has been trending, which led me to investigate why. The only thing I was able to come up with was a Tweet from The Walking Dead's official page from 2017. The post includes a gif of Rick Grimes (Andrew Lincoln) choking out Gracie's father (Joshua Lamboy) from season 8. As internet searches tend to do, this led me to go back to the episode and see if Rick actually said "Say uncle" during this scene.
On October 29, 2017, AMC aired the second episode of season 8, "The Damned," of The Walking Dead series. This episode, written by Matt Negrete & Channing Powell and directed by Rosemary Rodriguez, sees the Kingdommers, Hilltoppers, and Alexandrians join together to come against Negan (Jeffrey Dean Morgan) and his Saviors at the Sanctuary and other outposts.
The scene that the gif is from takes place a little over halfway through the episode after Rick and Daryl (Norman Reedus) split up to search the outpost. A man jumps Rick, and a fight ensues. Neither man can get up the upper hand until Rick can get the guy in a choke hold and then impales him on a bracket protruding from the wall. I have confirmed he does not utter the phrase; this was just the caption used in the Tweet below that was posted the night the episode aired.
During my re-watch, I was reminded about how chaotic this time period of The Walking Dead was. Negan was doing his best to take down Rick while all the communities were fighting together, coming at the Saviors from every angle.
During this episode, it would be discovered that the man who attacked Rick was just protecting his infant daughter. After killing him, Rick enters a nursery with animals painted on the walls; a baby girl is nestled in her crib and the name Gracie is painted on the wall. Rick looks unbelieving at the ground, shaking his head. Then he spies his blood-splattered self in the mirror hanging above the bed and has to look away.
As Rick leaves the child and continues sweeping the outpost for Saviors and guns, he comes across a familiar face from the Atlanta camp. Morales (Juan Gabriel Pareja) comes up behind him, pointing a gun. They recognize one another, but Morales has no fond feelings for Rick as he is now a member of the Saviors.
A bit of trivia regarding Morales: he was last seen in season 1, episode 5, "Wildfire," making his absence the longest of any character from the series. It isn't clear what the purpose of Morales' return is, as he will be killed in the following episode. Perhaps to show how much this world changes people.
Sadly, this episode also sees Eric (Jordan Woods-Robinson) shot in the stomach during the firefight. Before Aaron (Ross Marquand) becomes aware of this, he tries to save Eric, who was pinned down by Saviors, which Aaron runs down with a car. When he comes to Eric's side, he sees that he is bleeding profusely. Eric will perish from his wound in the following episode.
Gracie, the baby that Rick found, was eventually adopted by Aaron. He becomes an amazingly loving father to her, willing to put himself in harm's way to protect her.
It still isn't clear why this was trending, but it led me down a great re-watch of this episode. You can view all eleven episodes of The Walking Dead on Netflix.