Is it rude if you say to someone I think you're beautiful but your hair is in a mess and your shoes are untidy?

A bit...the criticism negates the compliment. And they’re probably well aware of the state of their hair and shoes.

I dunno, I love to be upfront...that is just your personal opinion though

Having to opinion is not rude. Telling them might be.

It's not rude, just ill-advised.

Yes. Very rude

Why would you though?