We had a thread about this a bit back. In the course of which I came across this entry in a dictionary, which I think is rather fun:

curmudjeon, n. Etymology unknown. In the first edition of his Dictionary Dr Johnson doubtfully suggests as the origin of the word, coeur méchant , giving as the source of the suggestion "an unknown correspondent"; Ash, the compiler of an English Dictionary a little later, misunderstood this & boldly explained the word as derived from "Fr. coeur, "unknown" & mechant, "a correspondent"!
A churlish, cross-grained, surly, ill-tempered, cantankerous fellow.