I think the idiomatic expression is:

Tu vis dans une caverne ou quoi ?

Variation courtesy of TonioElGringo:

Tu vis dans une grotte ?

('ou quoi' can be left implicit also)

Literally 'Are you living in a cavern or what ?'. The wording is not syntactically correct as it should be 'Vis tu' and not 'Tu vis', but this is an usual formulation for this expression.

Another variant could be:

Tu es resté au moyen-âge ?

This one is a little off from the rock idea, literally: 'Are you still living at middle-age ?'. It is mostly used to tease people uncomfortable with newer technologies.

I think the idiomatic expression is:

Tu vis dans une caverne ou quoi ?

Variation courtesy of TonioElGringo:

Tu vis dans une grotte ?

('ou quoi' can be left implicit also)

Literally 'Are you living in a cavern or what ?'. The wording is not syntactically correct as it should be 'Vis tu' and not 'Tu vis', but this is an usual formulation for this expression.

Another variant could be:

Tu es resté au moyen-âge ?

This one is a little off from the rock idea, literally: 'Are you still living at middle ages ?'. It is mostly used to tease people uncomfortable with newer technologies.

I think the idiomatic expression is:

Tu vis dans une caverne ou quoi ?

Literally 'Are you living in a cavern or what ?'. The wording is not syntactically correct as it should be 'Vis tu' and not 'Tu vis', but this is an usual formulation for this expression.

I think the idiomatic expression is:

Tu vis dans une caverne ou quoi ?

Variation courtesy of TonioElGringo:

Tu vis dans une grotte ?

('ou quoi' can be left implicit also)

Literally 'Are you living in a cavern or what ?'. The wording is not syntactically correct as it should be 'Vis tu' and not 'Tu vis', but this is an usual formulation for this expression.

Another variant could be:

Tu es resté au moyen-âge ?

This one is a little off from the rock idea, literally: 'Are you still living at middle-age ?'. It is mostly used to tease people uncomfortable with newer technologies.