man in the street vs Joe Bloggs

man in the street and Joe Bloggs both are nouns.

Word	Noun	Adjective	Verb	Adverb
man in the street	Yes	No	No	No
Joe Bloggs	Yes	No	No	No

As nouns, man in the street and Joe Bloggs are synonyms defined as:

Other synonyms of man in the street include Joe Blow, John Doe.

man in the street (noun)	Joe Bloggs (noun)
a hypothetical average man	a hypothetical average man