Tonight with your 13 to 17 year old
The prompt
“Is there an inside joke you have that would make zero sense to anyone outside your friend group?”
What to listen for
An eager retelling, even if it doesn't fully translate to you, is a great sign, it shows they have a place where they feel fully understood without having to explain themselves.
If they try to explain it and it clearly doesn't land the same way for you, that's actually the point, let them enjoy that it's theirs, without needing you to get it too.
If they say they don't really have one, that's worth noting gently, it might be worth asking about their friend group more generally another night.
What this tells you
An inside joke reveals a place where they feel effortlessly understood, which is at the core of feeling like they belong somewhere.