A "Dr. James' Diagnosis" is when someone - usually someone you know - tells you that they were diagnosed with either a crippling or lethal disease. They could state that they need to take illegal drugs in order to survive, or say they may dodge death if they are lucky. Sometimes both is stated. However, they are lying and unusually give no evidence why.
Of course, the "Dr. James' Diagnosis" is used to the benefit of the teller of a Dr. James' Diagnosis. Either for attention, or reason for doing illegal drugs without friends taking that into consideration.
The following is a conversation where James makes a Dr. James' Diagnosis:

James: "Sorry to say but I have lung cancer."
Richard: "Serious?"
James: "Yes, I'll need to smoke pot to survive."
by The Idiot Who Defines Slang. September 8, 2017
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