It's informal. If you said that, depending on the person, they may get uncomfortable or offended. You'd definitely not want to use it in a formal situation or if you fear that person you're referring to might get offended. Only use it in daily life if you know the ranges at which you can use it.
That's not to say you can't use it. It's dependent on your personality and the personality of who you're referring to.
Also don't use it on children. It's like saying "sweet/(juicy*) chick" on a child. (*juicy is not a correct translation for the meaning, more for the feeling of it in that context)