Euphemism - George Carlin

No one has more clearly and succinctly summed up and exemplified the definition of euphemism than George Carlin.  His outstanding example of how "shell shocked" evolved into "post traumatic stress disorder" tells us so much about how language evolves  -- and sometimes devolves -- and how clear meaning can be clouded by euphemisms.

Question:  How does Carlin's explanation of the term "post traumatic stress disorder" illustrate the down side of euphemism?