If my wife decides to wear something funny, my usual response is:
Baby, I love you very much and your happiness is more important to me than your looks. So, if you enjoy looking like a clown, that is alright, I love you anyway. You have to like the way you look, my opinion is secondary.
Haha I would like to say something like that, unfortunately she doesn't take criticisms about her looks too kindly, she will probably not talk with me for a week for this.