Well, if you insist, here goes:
(A non-bizarre delusion would be believing that your guru was raised from the dead, the exception for "culturally accepted response pattern" isn't for tulpa hallucinations, it is so that someone who feels the presence of god in the church, hopefully without actually seeing a god hallucination, isn't diagnosed.)
Here's the criteria for e.g. 295.40 Schizophreniform Disorder:
One of the following criteria, if delusions are judged to be bizarre, or hallucinations consist of hearing one voice participating in a running commentary of the patient's actions or of hearing two or more voices conversing with each other: Delusions, Hallucinations, (...)
Rule out of Schizoaffective or Mood Disorders
Disturbance not due to drugs, medication, or a general medical condition (e.g. delirium tremens)
Duration of an episode of the disorder (hallucinations) one to six months
Criteria for 298.80: Brief Psychotic Disorder
Presence of one (or more) of the following symptoms: hallucinations (...)
Duration between one day and one month
Hallucination not better accounted for by Schizoaffective Disorder, Mood Disorder With Psychotic Features, Schizophrenia
Criteria for 298.90: Psychotic Disorder NOS (Not Otherwise Specified):
Psychotic symptomatology (e.g. hallucinations) that do not meet the criteria for any specific Psychotic Disorder, Examples include persistent auditory hallucinations in the absence of any other features.
Where are the additional criteria for that? Wait, there are none!
In summary: You tell a professional about that "friend" you're seeing and hearing, you either get 295.40 Schizophreniform Disorder or 298.80: Brief Psychotic Disorder depending on the time frame, or 298.90: Psychotic Disorder NOS (Not Otherwise Specified) in any case. Congratulations!
Fair enough, if I had an imaginary friend I wouldn't want to report it to a shrink. I got hung up on technicalities and the point I should have been focusing on is whether entertaining one specific delusion is likely to result in other symptoms of schizophrenia that are more directly harmful.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.