Top Irish jump jockey Ruby Walsh has the given name of Rupert but is universally known as Ruby. Is this an accepted nickname for Rupert in Ireland or is the appellation an eccentricity perpetrated by his parents?
My American grandfather Reuben (1910-2000, mostly in the New York area) was widely known as Ruby. It’s not an impossible boy’s nickname.
Jazz trumpet/cornet player Ruby (short for ‘Reuben’) Braff, 1927 - 2003 is another one who comes to mind…
pfffffffft.
Rupert is not a common name in Ireland. It is so uncommon, in fact, that I doubt you could say that there is any “accepted nickname” for Rupert.
Who would want his or her son to be beaten up on the playground?