he's an ENFP

Is this about the thread where you wrote about your nephew who is also some sort of your best friend and with whom you tend to have heated arguments about various topics where somehow your argument for him never makes sense?

If so, and others ENFPs are welcomed to correct me, I can give you my perspective of argument with them, since my best friend is an ENFP. If disagreements you two have are about topics of for example evolution (something that's not of some big importance to neither of you two) then bear in mind that he probably randomly chose side, especially if that conversation started like this: he asks you "what do you think about evolution, do you think it's probable or not?", then you say "yea, I do believe in evolution" and then you see him taking air and preparing for a heated conversation with you where he will be willing to say almost anything even if he doesn't believe in things he's saying just for the sake of argument.

Over time I got to realize that for them that way of arguing about things is fun, and they actually don't care if they are right (with some exceptions when the topic is something very personal to them), they just want to discuss things with someone whose intellect they actually value and with whom they have impression that they are learning and expanding their own mind while attempting to help you do the same with yours. I do value their ways, but for me sometimes that way is not optional, or if my ENFP friend goes to far in that discussion with her arguments I just find a way to end it so nobody gets hurt. So if this is your situation with your nephew, I'd say to take his attempts to argue over things with you as a compliment.

 

My twin sister is an ENFP and she majorly bottles up her anger. It comes from their people-pleasing.

 

Nope, problem was on my side, I just didn't read carefully what you wrote and just assumed that you thought about what you wrote on that other thread.

If the problem with your nephew was not something that you caused but is something that is a consequence of bottled up anger about something else, my experience is that they handle very well when someone points them out that but only after the initial wave of anger is passed. Just wait for him to cool down a bit and ask him if he needs to talk to someone, offer just to listen about the things that make him angry. And even when they lash out on someone it's usually because that someone reminded them of other situation when they were hurt and felt anger but didn't allow themselves to express it. They just need some understanding and a good listening. Again that's only my experience with them, I might not be right about every ENFP about this.