Formal:
* Irrelevant: This is the most direct and formal way to say something is not relevant.
* Unimportant: This emphasizes the lack of significance.
* Extraneous: This implies that something is unnecessary or outside the main topic.
* Insignificant: This suggests that something is too small or trivial to be considered.
* Superfluous: This means that something is unnecessary or excessive.
* Trivial: This implies that something is unimportant or insignificant.
* Frivolous: This suggests that something is lighthearted and lacking in seriousness.
Informal:
* Beside the point: This means that something is not relevant to the current discussion.
* Off-topic: This means that something is not related to the current subject.
* Doesn't matter: This is a simple and direct way to say that something is unimportant.
* Who cares? This is a casual and dismissive way to express that something is irrelevant.
* Meaningless: This suggests that something is without purpose or significance.
* Pointless: This means that something is lacking in purpose or value.
The best word to use will depend on the context and the tone you want to convey.