Two presidents of the USA, the most powerful country in the world, in recent history gained ill reputation by not managing to keep their pants up. You'd think that if your efforts in life culminated in reaching that position, you wouldn't want to risk anything by being a pervert, but it's not so. The only difference between the past and the present is that nowadays people get caught, and when they do, there are consequences. Although it's a tiresome example, but do you actually think in the religious organisations there were no problems before our modern times with pervert employees, just because nobody ever reported anything?
Think for a moment how an adult woman could behave if some little, witless kid attacked her breasts. It would be different from how she would react if it was a man. What I am saying is that Roxy doesn't see the cretin prince as worthy of her attention at all. He might be five years old as far as she's concerned. By the looks of it, he indeed is so retarded that would about match his mental age. Roxy also didn't really take Rudeus so seriously as a man, even though she very much recognised his magic talent.
Btw, based on your reply, I fear you aren't doing well with trolls. They also harass people wishing for a maximum reaction. Nothing is worse for them than getting no reaction, only a ban or other disciplinary measure. Which is exactly what Roxy did with the imbecile prince.