This is my idea for what is going on in the world of Salad Fingers.
The Wake-Up Call refers to the end of Episode 5.
Salad Fingers is, in my opinion, transgender (biologically female). This explains having a teat and apparently having been a bride (before he came out). This also explains why he wasn't in the army; transgender people are often discharged even today. He is often referred to as "Mr. Fingers", reflecting his chosen gender, and refers to himself as Kenneth's older brother. I am NOT trying to connect this to his psychosis.
Fingers knows, somewhere in the back of his mind, that this is all a hallucination. This is shattered by the Wake-Up Call, when he truly realizes that this is reality. Confusingly, he actually does have hallucinations.
Right from the start, Cumberdale is different from the other puppets, being bald and with a stitched-up mouth. "Hubert C" is an anagram of "Butcher", and this is why he appears among frozen meat in Salad Fingers' unconscious dream in Episode 2. Notably, Cumberdale appears much more often in moments of insanity, does not have a parallel with a real person, and doesn't appear when Fingers is reliving events. Cumberdale is also wearing a straitjacket, adding to the idea that Cumberdale is the manifestation of Fingers' madness
Marjory is a manifestation of Fingers' happiness. Her taste (I believe it is "sparkles and sunshine dust", but I may be wrong) clearly represents good, but the real evidence is with Kenneth. It is no coincidence that Marjory appeared there, at perhaps the happiest moment in the series, especially since Jeremy would have also worked.
To be continued