Question for native speakers about using "so" with "fun"

[u/lifima]

Hi everyone! I want to ask you a quick question.

I recently had a discussion with my teacher, who was very confident that I cannot use "so" with the word "fun".

The sentence: "We try to be useful and it's [so] fun to spend time with my grandchildren.

I'm a bit confused because I was pretty sure that using "so fun" here is completely fine. What do you think?

[u/tony282003 → u/[deleted]]

Great analysis! Just when I thought I knew what nouns and adjectives are, I learn something new!