Why do people say Jesus H. Christ when they are mad. What does the H stand for in his name?
The Master speaks:
Who knows, it could be any one of these 
Not only does He not have a middle name, He doesn’t have a last name either.
Surnames are a product of the later Middle Ages, when Henry the miller, son of John the miller, son of Benedict the miller – each of whom had bequeathed the mill to his son – ended up becoming Henry Miller. My ancestry includes a lineage of Carpenters who got their name in about 1300-50 in precisely this way.
“Christ” is an epithet identifying Y’shua the Messiah (in the views of His followers) from Y’shua the tailor and Y’shua the rug merchant. If Jesus had been referred to formally in some secular document, he would have been Y’shua bar Yosef or Y’shua bar Miriam, using the patronymic (actually in the latter case the matronymic).
The “H” in “Jesus H. Christ” has no clear antecedent – and in any case it is merely a bit of blasphemous (in the literal sense) ejaculation. There is speculation, whether valid or not I cannot say, that it derives from IH[symbol]S[/symbol] – the first three letters of His name in Greek, iota-eta-sigma, with the H, representing a long E sound, being taken as Latin-alphabet H instead of eta.
“Christ” is derived from the Greek “Christos,” which translates the Hebrew “Mashiah.”
I’d always heard that his middle name was “of”.
Jesus of Nazareth