To be filed under problems you shouldn’t have anyway – using the same bar of soap for washing your face and, well, the rest of you.
The British (hence the spelling) have developed black/white, Arse/Face soap. Basically, oh, do we really need to explain it to you? Once you get it, you get it.
A few points grab us immediately, however:
Surely no-one still washes their face with soap; and
The British all take baths instead of showers, so regardless of which side of the soap they use, they’ll be splishing about in the lather anyway.
It’s largely a gag purchase. For some vulgar friend this holiday season for whom you can’t think of a real gift.