Lol, I got hung up on the first line. "the makings of a good relationship" and ran with it.

I guess the essence of what I wrote above is... How does this person act when things don't go their way? When they get what they want and you act the way they want, a toxic person will be as happy as a clam. They love you. But the moment a little adversity is thrown into the mix, ie. you disagree with them, criticize them, say something they perceive as a slight or even have an innocuous problem that you try to address with them, they will react very poorly. You have fallen out of step and need swift and merciless correction. They will use one of their favorite defense mechanisms such as the mini "silent treatment" or rage at you for having dared to inconvenience them or wrong them. They will scold and berate you or the offending person. Their reaction is so far out of proportion to what was supposedly done or said to them. This is their "shock and awe" tactic to ensure, in the narcissists case, their continuous flow of supply. So watch carefully what this person does when the going gets tough or things aren't perfect... When a baby is crying in church, when service is slow at a restaurant, when the neighbor parks in their spot. Mind you that the pd person can be quite adept at hiding this part of themselves in the beginning of the relationship. You have to watch closely to how they treat strangers who inconvenience them. It won't take long before they show their true colors as an emotionally immature, high conflict, toxic person and start aiming their venom at you.