It probably was a throwaway comment. Even if it wasn't, it was an error on their side, not yours. I used to be a lot more sensitive to comments before I really started to think about it. I thought 'Do I really believe that this person's aim is to hurt me?' - most of the time the answer would be no and I'd realise that they had just phrased something ambiguously and would probably be horrified if they thought they'd caused offence. In cases where I'd concluded that the comment was intended in a negative way, I would think back to see if I'd done anything to warrant it - if not, I would distance myself from this person, as I don't welcome negativity into my world.