It started ages ago actually. It was more a male thing as well. Older males would wear sandals with socks, so to me this will never be in style. The sports sliders are common with those who are athletic, so they can change out of cleats or "court" shoes before going on the street, not everyone does this for fashion reasons - or lack thereof depending upon you siding on this issue. It does look funny but the one that tops this is people going in public in PJ bottoms and their slipper - it actually drives my husband nuts, lol.