With no Kardashian/Jenner family holiday party to attend, new parents Justin and Hailey celebrated ... to change out of her PJs. Bieber wore blue striped boxer shorts (her husband's, perhaps?) ...

Hailey Bieber was recently spotted nailing a fun ... Her fitted pair included a pair of Alo biker shorts with a basic black crewneck t-shirt, likely from the same athletic apparel brand.

By Gil Kaufman Justin Bieber and wife model Hailey Bieber have been judicious ... a moon shot and a snap of the singer in just his boots, boxer shorts and a hat hopping out of an ice-caked river ...