Hey, noFlippers? Those are what some people wear when they go swimming and snorkeling.
So residents and married/committed relationship guests take their shoes off, but unmarried/single guests leave their shoes on.
Here it's usually whatever the house rules are. I take my own shoes off and wear slippers around the apartment. If I leave the apartment, I put shoes on. Everyone else can leave their shoes on as long as they wipe their feet on the mat inside the door. Otherwise they'll get their socks full of cat hair.
I used to have a friend who insisted on going barefoot in my house (when I lived in a house). I finally told her to keep her shoes on, since that was when I did a lot of needlepoint and other sewing and it wasn't unlikely that I'd dropped a few pins and needles on the floor. I didn't want her stepping on them.
I meant that if the guest is romantically involved with their host they'd naturally be allowed to act as if they were in their own house=>take their shoes off. After all, they'd likely have taken off more in the same place.
And not as a formal rule, eg if there is an affair which isn't known to others, the guest who is secretly in the affair won't be cosmically forced to betray it by having to take their shoes off