“How rotten and fraudulent when people say they intend to ‘give it to you straight.’ What are you up to, dear friend? It shouldn’t need your announcement, but be readily seen, as if written on your forehead, heard in the ring of your voice, a flash in your eyes – just as the beloved sees it all in the lover’s glance. In short, the straightforward and good person should be like a smelly goat – you know when they are in the room with you.” Marcus Aurelius, Meditations.
My stock reply to a friend who starts a sentence with ‘To be honest…’ is to thank them for their honesty. I wouldn’t expect anything less of them. But what are they really trying to say? That perhaps they worry that their opinions might not be popular or readily-accepted, and so they need to signal that they feel a little personal discomfort in saying it. Or is it a pre-emptive move, warning the listener that their ‘honesty’ on this occasion may cause distress or offence, but that you have been warned, so don’t overreact and shoot the messenger? What do you think, as, after all, this is just in my humble opinion. No offence!