dress code is also completely made up bullshit that has no reason to exist in the modern world
This is a ridiculous notion.
There are plenty of people that would show up to work without bathing while wearing sweatpants and teddy bear slippers if they were allowed. Source: I worked in a low-end call center fresh out of school and a good quarter of the people actually did dress like this most days.
Without a dress code a business has no grounds to address the situation.
If I walked into a new grocery chain or restaurant and everyone was dressed in dirty house clothes the best reaction I would have is to ask someone if this was a joke day. The more likely reaction would be just turning around and walking out.