Game of Thrones features such fantastical creatures as dragons, undead monsters, and magical tree people, but the one thing that fans have trouble dealing with is the sight of a Starbucks cup in Winterfell, which appeared in the latest episode.
The most recent episode of Game of Thrones as of the time of writing is "The Last of the Starks", which is the fourth episode of season eight. The episode follows the defeat of the Night King and the destruction of his army, which leads to a burial scene and a feast in Winterfell for the survivors. The battle against the dead is over, which means that the living are given a chance to enjoy life, even if it's only for a few hours.
It was during the feast that the fans noticed something out of place on the table at Winterfell. At around the sixteen-minute mark of the episode, there is a moment where Tormund is talking about how great Jon Snow is while Daenerys looks on in the background. The fans noticed that the Khaleesi seems to have abandoned the drinking horns and goblets of her allies and has gone for something more modern, as there appears to be a Starbucks cup on the table in front of her.
The contents of the cup have yet to be revealed. It's possible that Daenerys is a fan of the Espresso Con Panna, or maybe she prefers an Iced Skinny Mocha. The canonicity of the Khaleesi's taste for Starbucks has yet to be determined and it's possible that her coffee preferences will be revealed in The Winds of Winter.
It's always embarrassing when a movie or TV show features an anachronistic blooper, such as the jeep that appeared in Braveheart or the gas canisters in the chariots in Gladiator. The producers on the show had to film an incredible amount of content in a short period of time, so it's only natural that a few mistakes might creep in. The fans are at least more understanding of a cup accidentally being left on the set than they are of the episode being too dark to see. The only question now is whether the producers can squeeze some extra money to digitally remove the cup for the Blu-ray version of the episode.
Game of Thrones is one of the most expensive TV shows of all time and unlike a lot of other shows, it's impossible to fit any kind of product placement within the story in order to offset any of the production costs. It would be extremely out of place for Tyrion to hold up an iPad with the Apple logo conspicuously in the middle of the screen while he drafts his battle plans. There were other HBO shows that went overboard with the product placement (most notably The Sopranos) and Game of Thrones managed to avoid any conspicuous ads until today when a production blooper accidentally left a Starbucks cup in Winterfell.