Having met many people in my lifetime and having dealt with a good percentage of them, as well as having had personal relationships with some ... on occasion a delusional person crosses my path. I think the most frustrating element of this type of person is it is impossible to have an amenable discussion or a meeting of the minds with him/her. Impossible. Below are some descriptions of delusional disorder taken from WebMD.com.
"Delusional disorder, previously called paranoid disorder, is a type of serious mental illness involving a specific kind of psychosis. Psychosis is the inability to tell what is real from what is imagined. The main feature of delusional disorder is the presence of delusions -- unshakable beliefs in something untrue. People with delusional disorder experience non-bizarre delusions, which involve situations that could occur in real life, such as being followed, poisoned, deceived, conspired against, or loved from a distance. These delusions usually involve the misinterpretation of perceptions or experiences. In reality, however, the situations are either not true at all or highly exaggerated."
One of my previous neighbors, in her late forties and living with her mother, was delusional in the sense that she believed a film star was going to marry her, she was actually planning on it, said they were engaged. (I've had two friends like this.) When I asked her if she'd heard that the actor had just married someone else, she said he did it for publicity and it was a front. Now, I knew there was no way that hunk would have had any interest in my neighbor, just not possible, and I won't go into the reasons here. Just believe me, it was not possible. She was delusional, big time. This is called:
Erotomanic Type: delusions that another person, usually of higher status, is in love with the individual
Another quote from WebMD ...
"People with delusional disorder often can continue to socialize and function normally, apart from the subject of their delusion, and generally do not behave in an obviously odd or bizarre manner. This is unlike people with other psychotic disorders, who also might have delusions as a symptom of their disorder. In some cases, however, people with delusional disorder might become so preoccupied with their delusions that their lives are disrupted."
One other type of delusional persons I've known are those that don't see things as they really are, feel they are being mistreated, creating their own reality and nothing can dissuade them. Exaggeration is a huge part of their dialog. They'll even take what is said or done and twist it, putting their own slant on it, and then pass that on to others. Very perplexing to say the least, but nothing you can change or address. They also pick and choose what to remember. They can't tell what is real or imagined. This is called:
Persecutory Type: delusions that the person is being malevolently treated in some way
One person I knew would make a statement about something that you wouldn't necessarily agree with and didn't care to comment on, and if you didn't say anything she would keep talking and would interpret your silence as if you were in agreement. My friends and I knew the person did this to everybody, we all knew it. So if she said so and so told her this or that, which was her habit, we knew better. She was delusional.
I also knew a gal who believed evil witches were after her. Black crows signified their presence, even black SUVs passing by the house carried witches. Oh boy! That was quite an experience ... she was a roommate, and very paranoid and delusional in several ways.
Then there are those who believe they have serious medical problems and exaggerate every time a minor illness strikes. We've all known this type of delusional disorder existing in at least one of our friends or family members. I've known quite a few. This is called:
Somatic Type: delusions that the person has some physical defect or general medical condition
Sad to say . . . a delusional disorder is harmful to the one owning it AND to those who are on the other side of it. No one wins. As an onlooker or recipient, you have no defense from a delusional person's attack, especially if he/she isn't being treated. But realizing that the person has this disorder and separating yourself from it's effects, if you can, is the best recourse for you. Not easy sometimes, and not very pleasant to end contact, but in most cases, necessary in my book.