A fun and light-hearted episode that seems to have struck a nerve with some particular people. It features the characters "flossing", aka performing a dance that is typically associated with the game Fortnite (although it was already a thing before Fortnite, people!). I am still part of a generation that used this dance move when it was popular, though I never saw the appeal in it. But this is a show made for kids, and adults being enraged over something as harmless as a dance is hilarious. When I was young, the Gangnam Style was popular and everyone was doing it, us kids included. They are harmless, silly dances, nothing more.
Furthermore, I think that everyone disappointed by this episode missed its core message. It is not about flossing. It is about not being a know-it-all, not ruining harmless fun for the sake of being correct, having empathy for others and prioritizing friendship over your ego. "Grannies" teaches a great lesson just like other episodes of Bluey, and I hope people can see that this is more important than their pointless annoyance at a "cringe" dance!