Most of what is said is said to gain a specific advantage. If there is an attempt being made to insult you, most of the time it is just to distract you from the goal. The other person could well use the same lines on the next person they deal with. It is "shop talk" to them, nothing else. Just put some space between yourself and your positions. The attacks are on what you seek, not on who you are. By not allowing yourself to be intimidated, or drawn in, you can keep your focus on what you should be thinking about. When your opposition realizes you can't be intimidated, they usually run out of steam and become a lot more rational. You have to be prepared for it.
The world is full of unenlightened people who will try to insult you. If they are being unpleasant, maybe something else is going on in their lives that has carried over into your dealings. Always try to separate the issues from the person. In short, don't over react.
Don't try to tell someone how to conduct his or her own business. People resent being told what to do, especially when you are delving into their area of expertise. Instead of projecting what I think the other side should be doing, I discuss what seems to be the norm at that particular time. This gives them a chance to explain to me why there is a problem and prevents me from insulting them by trying to tell them their own business.