human buffer
the perfect guest who is invited to family get-togethers for the sole purpose of buffering the in-laws from the rest of the immediate family.
Hey, let's invite your brother's new girlfriend for Christmas this year. She was the perfect human buffer at Thanksgiving. She laughed at and made all the appropriate comments during the in-laws' nonsensical ramblings and stupid jokes that all the rest of us have heard a thousand times. She rocks!!!