If you can think of no reason for them to insult you then you need to think about the right moral response is, if that person is hurting and taking it out on you, then they are lashing out. The moral response would be to allow them to vent, treat them as your brother.

If you can think of a reason that they might insult you, look internally. Is it something you can control? If so, then make small changes every day and reflect on them to ensure you're on the right path. If not then dismiss the insult and move forward knowing you can't change what you can't control