My nephews love to wear nail polish. Actually, not so much recently, but they used to. My sister doesn't own any, but never minded if I did their nails when they were at my house. My brother-in-law freaks out - he must have read that it makes little boys gay in the same place your sister's boyfriend did. So sad to get all riled up about nothing.
Now my older nephew won't wear it, but he'll paint my daughter's nails for her. I'm sure BIL wouldn't like that either...
"Home is where the heart is, no matter how the heart lives." - PP&M