touch grass

This phrase comes from the netiverse and was originally directed at people who were thought to have spent too much time online (and it was showing). They were therefore advised to go outside into the real world and touch some grass to reconnect.  Before touch grass! the insulting expression with the same meaning was go outside!.  Somewhere in 2019 touch grass surfaced and become popular on Twitter in 2021.

It has generalised somewhat to be applicable in situations where you think someone is saying something weird. It might also be that they are revealing their personal obsessions. In this context it is the equivalent of Get real! and meant to bring them back into the normal range of ideas and opinions.