Users of a Stack Exchange Q&A site generally do not need or even want a 'fun' tag.
On a technical level, tags are supposed to indicate what the question is about. A question tagged 'fun' isn't likely to be about "fun", so that type of meta-tagging (indicating why the question was asked rather than what the question is about) is widely discouraged.
Stack Exchange sites are set up to solve specific problems in a field of expertise. While there's nothing inherently wrong with entertaining and social discussions, those types of conversation starters are not really what we are looking for here. It's even debatable whether we even need a 'trivia' tag, but it seems well suited to questions about the product, and the culture/language surrounding it.