The only reason he was cordial in pm was because he was in the position of authority or power in that exchange. People wanted something from him, his opinion or advice etc. Approach him as an equal and see how long the conversation lasts, we had pm’d many times and each time I’d question him for sources or other information he hinted at communication would cease. Don’t get me wrong, I respect the guy for his knowledge but he was an asshole of the highest order.
Now on topic:
There are a lot of things he can do to direct negative energy in a passive aggressive way. He can spend time visualizing, fantasizing or even planning out how to do a ritual that will cause harm. I’ve seen negative consequences happen to other albeit in varying degrees of intensity but the point is directing energy can cause desired change. Is it as powerful as a spell or ritual definitely not but if your skill set is not up for bigger work it is an option.