sidewalk friend

A sidewalk friend is the one in a group who automatically moves behind on a narrow sidewalk, assuming the least value in themselves.

Person 1: Hey, who’s that behind you?
Person 2: Huh? Oh, her? She’s nobody, just my sidewalk friend.

Sidewalk Friend

Noun: The person who has to walk behind on a narrow sidewalk; the least favorite in a 3-person friend group who often feels like they don't belong or are unappreciated.

Person 1: even when I'm with them, those two sometimes act like I'm not even there. I'm their sidewalk friend.