It’s actually shown quite a few times.

The episode where Peter gets to visit the Pawtucket Patriot factory.

A cutaway gag of Brian fighting a mirror thinking it’s another dog and Peter doing the same after seeing Brian unconscious.

The episode where Peter tried to build a pool in his yard.

It’s been in a few more but I can’t recall since I haven’t watched in a few years but they definitely show it more than once.