"You should shave your mustache"
/I was born with really dark hair and had not yet discovered the luxury of waxing or bleaching.
There was this one guy I had a crush on in middle school, and we would IM back and forth after school sometimes.
He randomly said to me one day, "You have a mustache. You should shave it."
I did. And to this day, it's still one of my biggest insecurities.