That's part of the "mom code of ethics".
Don't crack your knuckles...
Never sit on a boys lap.
You'll get hemorrhoids if you sit on cold concrete.
Keep it up and you'll go blind.
Your face will stay that way...
"If you go out make sure that you wear clean underwear...." Where did this saying originate?
Well I do know that thought has been around for a long time. Probably was an old wives tale to begin with. Hygiene in general was bad for a huge chunk of history. There was probably a false correlation between certain ailments and dirty underwear.
Funny story. My mom in law was on the bus one morning on her way to school. She was in high school. She saw her mother chasing after the bus erratically. Honking her horn waving at the bus to pull over. The bus driver did, her mother pulled right up to the bus door which the bus driver thought was some kind of emergency. She marched on that bus and in front of a whole busload of her peers her mother asked her if she remembered to wear clean underwear. My mom in law is 73, her face still colors at the memory.
A leaflet on personal hygiene, maybe?
Paramedics. If you get into an accident and your clothes have to get cut off you dont want the EMS crew looking at your dirty undies!
When my mom told me that, because I might be in an accident, I told her it would not matter because they would be dirty anyway if I was in an accident.