Backpfeifengesicht (roughly, "BACK-fifengehzeekt") is a German word.
German words can be so wonderful, expressing depths and nuances of emotion in single words.
Backpfeifengesicht. A face in need of a slap.
You know it when you see it.
I mean, c'mon. You...KNOW IT...when you see it. Downturned lips from a lifetime of pouting about this or that. Weak cheeks and chin. Kind of amorphous features that simply shout, "Of, ffs, just slap me!"