In a way they're very smart but in a way there quite stupid. They're clever in finding ways of conning people and getting their trust but they make some really stupid/irrational claims and it doesn't seem to occur to them how they may be caught out (for some reason they don't seem to have any fear of being caught whereas I would be scared of being found to be lying).
For example I had an N relative who claimed to be such a good swimmer and that she even raced against the sister of Dawn Fraser (one of Australia's most famous swimmers) but on one occassion she asked whether you could stand up in the pool of the place we were staying. When I said that you couldn't she said quietly to herself "oh no". I was a bit surprised to hear that from someone who claimed that she was such a good swimmer.
She also claims to have worked for many government ministers and even says that she was even at the meeting at which a certain state premier resigned. Unfortunately for her that premier's biography happened to be in my school library and it said that he resigned in 1986. The only problem is that she married and moved interstate about five years earlier so there is no way that she could have been at that meeting.
Unfortunately I have two narcissistic relatives.