Oh, Manchester, So Much To Answer For

I hope someone, anyone, can explain the phenom of wearing your house slippers in public to me. Today at work, I saw a young woman - presumably going into a lawyer's office (I think she had "the whiplath") - wearing Spongebob slippers. And then tonight at 7-Eleven, a woman entering as I was leaving was wearing her house slippers, as well (along with a fetching plastic rain bonnet-type thing on her head). Since when do you wear slippers out to the store (or, as the case may be, to "tha sto'")?! Absurd.