Mr. Mencken should know that the profane begob and begorrah are unknown to Irish people: they are words employed only by jokesmiths in cheap burlesque and pink papers. It is rather in habits of pronunciation, of syntax, and even of grammar, Mr. Mencken continues, that we have been influenced by the Irish.
At this point, Idiomation was unable to find an earlier published version of begorrah than the one in 1839 despite the Merriam-Webster Dictionary claim it was first used in 1715 without quote the source material where it can be found.
Saul Goodman:
Faith and begorrah! A fellow potato eater! My real name's McGill. The Jew thing I just do for the homeboys. They all want a pipe-hitting member of the tribe, so to speak...
A very nice lady who currently hails from New Jersey but is like myselforiginally from Ireland reminded me of this sad excuse of a phrase. Alittle Google-digging reveals that the word begorrah may have itsorigins in the 18th century or earlier; perhaps as a euphemism for "byGod". The closest Irish word I can find to it is Goradhwhich means heat or heating (rinne mé a goradh cois tinetranslates as "I warmed myself by the fire").