Reading between the lines, Radical Honesty is a type of practice where one is constantly working to engage with every moment and every interaction, and not to always default to being "nice". Most people aren't aware of what they are thinking and how it shapes them. To be radically honest is a form of tapping into the mind stream and checking it.
Through being constantly aware of the mind's contents one is in a better position to elicit interesting relationships, beyond just mere niceties.
So if someone comes up to one of these radically honest people and tells them they are a pretentious self-important little jerk who is too full of themselves to be worth even contemplating getting to know they will think "Oh! What a refreshingly straightforward person, I must elicit an interesting relationship with them". I don't think so.
It is a process. One doesn't become radically honest with oneself until one notices how the body physically responds to criticisms.
Toastmasters is a good example where I keep noticing the better toastmasters actively solicit criticisms. Even if the message was "your speech was boring" is sufficient to prod them figure out how to improve it.
Through being constantly aware of the mind's contents one is in a better position to elicit interesting relationships, beyond just mere niceties.