I was flabbergasted how my colleague hadn't even heard of a certain app I thought virtually anyone at my age would be familiar with – unless they are living in the Stone Age.
I wanted to say jokingly in French:
In case you're living under a rock, this app allows you to ...
In English, you use this expression to tease a person who doesn't even know the first thing about what seems like common knowledge today, seemingly oblivious to anything but their interests, or perhaps simply preferring a secluded, hermit way of life.
Below is what I actually said to her, but I couldn't come up with something more straightforward right there and then. How do you idiomatically express this "living under a rock" idea in French?
Quoi ?! Qu'est-ce que ça te coûte de sortir un peu plus souvent, ma petite troglodyte ! ...