I think that this is only applicable for those guys who show themselves as decent in the public. They won't physically abuse us but they would mentally abuse by asking our mobile numbers!!
Let's be practical about this conversation! If they are asking from all the women's then that's a different mentality, But if it happened very specifically and very polite way then i assume this could be a love that he's trying to reach you in a different channels to express his love! No matter how brave is the men, when men proposing to a women about his true he love's is absolutely a very terrible situation and they'll be ridiculously weak during that time. They to be steady and brave, But mostly they flopped! such situations will make the women to think in a very different perspective.

WOULD THEY LEAVE US IF WE CALL THEM AS BROTHER?
Again, if the men is seeking a different needs then this won't work, because he won't even think about it! but, again let's be practical! if he's trying to propose you then 50/50 chances he could leave you.