Not exactly minhagim, but for sure familial:
My parents always called slippers ‘bedroom shoes. No one else I knew used the phrase. Then I grew up, became frum, moved to Monsey, learned ah bissele Yiddish, and learned the phrase ‘stenk shiach.’
Another phrase that I never heard outside of my family was ‘on the riggle’. Other people locked the door, we put it ‘on the riggle’. Then as a Mommy in Monsey I was asking a more experienced Mommy how to keep my toddler from making trouble in the bathroom, because he had just reached the door-opening stage. She told me “You need a riggle” and presented me with a hook-and-eye lock to put on the outside of the bathroom door.