The term 'narcissist' isn't an insult, it's a name for a personality trait which includes:
Sense of entitlement, deserving of special attention
Manipulative behaviour.
Need for attention and validation
Lack of empathy with the needs of others
Unwillingness to take responsibility for actions
Disturbed self-identity
Need for control
etc.
Anyone who has ever been in a relationship with a narcissist will recognise those traits, and how damaging they are.
The behaviours typical of a narcissist are also typical of the behaviour of the trans movement in general - you can check off each item on the list and find obvious examples of it, from everything from toilets to the law having to defer to trans demands, to the non-factual self-identification with the opposite sex.
The hyperbole about 'genocide' and 'literal violence' and the threat of suicide if their demands are not met are also narcissistic behaviours.
There has to be some explanation for how an unscientific, obviously untrue statement like 'Transwomen Are Women' has been able to take over societies to the astonishing extent that it has.
Since the transgender movement can't rely on science or justice or fairness to bolster their campaigns, there must be something going on that has allowed such an unlikely and obviously flawed campaign to be so successful.
Narcissists are excellent at controlling personal relationships, and making otherwise sensible people stay with them and make excuses for their abusive behaviours; they often do this by 'gaslighting', inventing a false narrative of reality which makes them the central character in all situations, and the hard-done-by victim in any conflicted situation.
Sadly it works very well, too well in many cases. But if you can identify the emotionally abusive person as 'a narcissist', i.e. having narcissistic traits, it's not an insult, it is an understanding that helps break the control they have over you.
So identifying the narcissistic behaviours used by the transgender movement in general is more of a analysis, an awareness, an explanation, than an insult.