"Hail fellow well met" is a somewhat archaic English idiom used either as an exaggerated greeting or referring to a person who is sociable and constantly making an effort to win friends. The Oxford English Dictionary (OED) gives a 1589 quotation for this phrase as a friendly greeting. The OED also gives quotations for the related phrase "hail fellow", a greeting that apparently dates to medieval times. "Well met" appears to have been added to the phrase in the 16th century to intensify its friendliness. This additional term seems to derive from the concept of "good to meet you", and also from the meaning of "meet" as something literally the right size for a given situation.
In modern English, the idiom is used as an exaggerated greeting or as a description of a personality type. The twentieth-century English novelist W. Somerset Maugham frequently used the term in his novels and short stories to describe male characters of a genial, sociable, and hard-drinking temperament. Modern use of the term tends to be deliberately archaic, with overtones of over-familiarity in the person (almost always male) so described, or as a deliberate, tongue in cheek term of endearment, heightening the effect of the greeting of an unexpected friend when as in "the only friendly person here" or to remark that there is a friend in an unfriendly atmosphere. It can also be used as a pejorative to describe a person (again, usually male) who is skilled at making superficial friendships or can ingratiate themselves quickly with any company at hand. The OED gives an example from the 17th century of the use of "hail fellow" as a description in a similarly pejorative manner.
It is also cited as "heartily friendly and congenial, comradely, hail-fellow - characteristic of or befitting a friend; 'friendly advice'; 'a friendly neighborhood'; 'the only friendly person here'; 'a friendly host and hostess'."[1]
James Joyce used the phrase "Hail fellow well met the next moment" in Ulysses to describe newspaper men.