It’s an absolute travesty, and the poor individual is gently mocked behind their back as they move around, blissfully unaware. It’s sad really, as they are almost certainly a nice person.
Why, you ask, are we talking about socks and sandals?
Because they set the same first impression as your mismatched business stationery.
They imply a lack of style or even of having given up caring, and they set a certain impression that most don’t really want…even if it has become a comfortable habit!