The phrase ‘so fun’ is commonly used in casual conversation and informal writing, but its grammatical correctness can be debated. Traditionally, the word ‘fun’ is classified as a noun, and many traditionalists argue that it should be used in a more structured format, such as ‘so much fun’ or ‘very enjoyable.’
However, in modern usage, particularly among younger generations, ‘so fun’ has gained acceptance as an adjective. This shift reflects a broader trend in the evolution of language where conversational expressions often challenge established grammatical norms.
Ultimately, whether you choose to use ‘so fun’ depends on your audience and the context in which you are communicating. In casual settings, it’s widely understood and accepted, while in formal writing, you might opt for the more traditional phrasing. Language evolves, and what’s important is effective communication.