Dealing with a narcissistic ex is no fun. Oftentimes the best thing to do is to ignore them. This strategy may be the best for a variety of reasons.
He may be acting in this way to gain your behavior
When you give attention to a narcissistic ex, you may be playing right into his hands. Many people who are narcissistic want attention, even if it is not positive. When you reward him with this, then he may be more likely to continue the behavior that you do not want to see. You may feel like it is your job to reform him, but he is now your ex. You do not have this role, and the more you try, the more you may actually be preventing him from seeing it. Sometimes being ignored is what makes a narcissistic person realize a little of their behavior.
It is unhealthy for you
Dealing with a narcissistic ex can be emotionally draining. You should not have to deal with this. It is not fair. When you are in a relationship, then you need to take both the good and the bad, but now that you are no longer in a relationship with the person, you do not have to be with someone who is going to think only about themselves or be self-serving or vain. A narcissistic person does not tend to think of those that are around them, and he may hurt you again and again. You do not have to let them do it.
You may feel like nothing you do can get you away from your narcissistic ex, but ignoring him can. You may be very much bothered by his actions, but when you ignore them you may find that you can put some distance between yourself and him. Suddenly when you are not as emotionally involved, you may find that the actions do not bother you as much. You may start to see them for what they really are - inappropriate actions by someone who thinks too much of himself and is not considerate to others. It can help you to move on if you ignore this behavior. You may be able to find a new healthier relationship instead.
Engaging a narcissistic ex may just make things worse for you and keep you chained to an unhealthy individual. For the reasons above, consider ignoring him and his behavior.