It didn't really affect the service, so not a big deal to me, but I thought it really odd. Don't think it was a broken shoe (or toe) because he had them on at the beginning of the flight (through the meal service), took them off for some time, then put them back on before final descent, and they seemed just fine. I don't normally look at the FA's feet, either, but noticed he was in socks when I went to the lav about midway through the flight. Maybe just a quirky FA.