How do you tell a person they have NPD?

Let's say, hypothetically, that there is this circle of friends. And let's say, hypothetically, that this circle of friends all have an acute awareness of NPD, and have experience in dealing with persons afflicted with NPD. And let's say, hypothetically, that they all have some degree of narcissism themselves (because the truth of it is, they really are unique, and smarter and better looking than the average bear) ;)
But let's say, hypothetically, that one of them is flying their red NPD flag really high and waving it all around. Let's say, their narcissism has become full blown NPD. Let's say that every interaction with them leaves you feeling insulted and abused. Does one have an obligation to call a spade a spade? How can a person lovingly approach this subject with the NPD? Let's say we want to really give them the benefit of the doubt, and believe that somewhere inside of them is a soul, and that if they are putting energy into educating themselves about NPD and educating themselves about healing that they should be given the knowledge that their own NPD is RAGING! so they can focus on healing/cleansing that toxicity within themselves.
Would an intervention work? The entire circle of friends sharing how the NPD affects them?
Are there any alternatives?
Love~