“What the dog doin” grew out of a viral video where the speaker spots a dog and asks the question in disbelief, and the phrasing quickly became a meme caption across TikTok and Twitter. People began posting it under clips of dogs caught doing odd, guilty or chaotic things, and the audio followed as a reaction sound. Its deliberately casual grammar is part of the joke, and it remains a go-to punchline for pet content because it fits almost any funny dog moment.