The first step should always be to let your partner know that the comment they have made has hurt you because if it has hurt you, then it is worth addressing. This allows for both of you to face the issue head on rather than walk around it, as it could be that their comment was phrased wrong or miscommunicated. Your partner can then clarify and reevaluate what they said, especially why they felt the need to “be honest”, while also allowing you not to internalise or overthink.
put yourself in their shoes and consider what you would do
So, if you ever find yourself beginning a sentence with “can I be honest”, the best thing to do is to step back and think whether what you are going to say will be helpful or harmful to the person it is aimed at. A way to do this may be to put yourself in their shoes and consider what you would do in the given situation or how you would react if someone made your comment to you, because sometimes an opinion can do more harm than good.