Delusional Aficionado Syndrome 

Not a real disease able to be diagnosed, DAS (Delusional Aficionado Syndrome) is a sophisticated medical slang term used to describe the state of mind of wanting to only speak well about something or someone a person is suddenly or has been obsessed with for a long time.

For example, in the case of a musician, the aficionado might hear one song he becomes entirely enamored with it and slips into a state of thinking that this artist is the best to have ever existed. The aficionado will then deal with this state of new found love by purchasing all the albums by the artist and recommending them to everyone he knows. In its highest severity, the afflicted aficionado will constantly talk about the artist and/or song even to the point of trespassing into other people’s conversations in order to spread the word about the music. The aficionado will become enraged (rarely to the point of violence) if he hears someone else say anything negative about his idol. If any negative telecasts enter the television/radio airwaves or the internet concerning the musician (especially his death), the aficionado will enter a massive state of denial.

The aficionado may or may not be aware of his DAS. It depends on the severity of the delusional behavior.

References:
"This Bloke, Right Here." (A pseudonym for the person who first coined the term while giving a review of the Exodus album by Utada Hikaru on the first of February in 2010.)

This Bloke, Right Here: "I do not have Delusional Aficionado Syndrome. This album truly deserves five stars out of five!"

Delusional Aficionado Syndrome by IareWHITE February 1, 2010