po-faced

adjective2

1. •
   (UK) Wearing a particularly stern and disapproving expression; humourless; priggish.

   • Nae hassle man . . . I'll git oaf the skag, and Saughton's barry fir hash. It'll be a piece ay pish likesay . . . he sais, as he's escorted away by a po–faced labdick. — 1993
2. •
   (UK) Poker-faced.