How would you explain the Meh button (and the Meh faces) to a newcomer?

dave thought this was worth mentioning said

We’re always thinking through how new people experience Meh. What’s obvious and clear to them? What’s confusing? What doesn’t get noticed at all?

If you told a friend to come to Meh, what would you say to them about the Meh button (why it’s there, what it’s for, what it does) and the Meh faces? I’m not looking for the official “here’s what we, as a company, should say” - I’m actually wondering what you’d say to a friend about it (or if you were ever shown Meh by someone, what they said to you about it).