Over at a website called Chateau Heartiste*, the anonymous author has this to say about the above picture:
The Germans have a word (the Germans always have a word) for “a punchable face”: Backpfeifengesicht.
That's rather hard cheese on feminism-boy, but we'll leave that aside for a moment. I found to my surprise that Backpfeifengesicht has an active double-life in English, with an eager crowd of Teutonophiles spearheading a movement to bring it into English to join Earworm, Weltschmerz, Fahrvergnügen, and other recent imports. Problem is, though, that nobody has any idea how to pronounce Backpfeifengesicht. The consonant-block 'ckpf' is, safe to say, not one many English-speakers have encountered, although it's far from the gnarliest that German has to offer.
My advice is simple: as with all German words, it's pronounced exactly as it's spelled, no matter how impossible that may seem at first.
* As for the sentiment expressed by the sign, I have emphatically no comment.