The term that Stephen uses for his "nuncle Richie" probably indicates not just familial familiarity but also ridicule. Reference works identify "nuncle" as an obsolete form of "uncle." There is some reason to suppose that it is still occasionally used in Ireland, but the memorable use of the word by the Fool in Shakespeare's King Lear suggests that Stephen is using it with disrespectful intent.

John Hunt 2023

The Fool and King Lear, in a 2009 performance at Wake Forest University. Source:

Alec McCowen as the Fool and Paul Scolfied as Lear in Peter Brook's 1962 stage production for the Royal Shakespeare Company.