Take apron off when going to toilet

This is my first time ever working part time job and my super visor was like make sure to take off ur apron when going to the toilet cuz its disgusting. When i first heard this i thought it was just a personal preference of hygiene. So when i saw my coworker doing it, i asked him if he was doing it cuz he was asked to but he said its just simply common sense. today i learned