How would you feel if a man said he could see you underwear? Please read first

So I figured we could use a change of pace in CC...

My dad found himself in a weird position earlier this year and we were talking about it again today so I figured I would like to hear some other opinions for fun

So my dad owns a flooring store, and before COVID-19, he would regularly see product reps. (Probably once a week.) This feild has been primarily male until the last few years.

Well in February he had a female product rep come in and you could see her underwear through her white skirt. The unofficial uniform for product reps is business to business-casual

My dad contemplated telling her because

1.) he knows she doesn't work with other women so he wasn't confident another female would tell her

2.) He knows how hard it is for women to get respect in the work place so he didn't want her to get ridiculed by male co-workers.

3.) He would want someone to tell me if I was in that situation and didn't want to be showing my underwear.

Ultimately, he decided that since he's 56 and she was about 25 that would've been too creepy to say something. But we still talk about pros and cons of saying something.

What would you do assuming it was the opposite gender? Do you think he should have said something?