The phrase old fogy is bothering a man from Clonmel who describes himself as one. "Of unknown origin" is all his dictionary has to offer about the noun, and I am asked if I can do any better than that.
Oxford guesses that it may be related to the 18th century slang word fogram, old fashioned, antiquated person, and admits that the origin of the slang word itself is unknown. I personally think that fogy is related to the Scots word foggie, (same pronunciation), from Scots fog. This particular fog is Scandinavian in origin, and has survived in Norwegian as fogg. It means weak scattered grass that grows in a damp meadow. Hence, figuratively, an old person.
An early occurrence of fog is found in the Anglo-Latin fogaglum, the privilege of pasturing cattle on fog. There is a small yellow bee, called in Scotland a foggie bummer and, a foggie bee, so named from its rough appearance, as if covered with moss, according to the EDD.
At any rate, the word fogy became common in the last century. In England and Scotland it came to mean an invalid soldier, and in Ireland specifically a pensioner of the Royal Hospital in Kilmainham. Lover had "He was just like a cut-down fogy" as far back as 1848, in his Legends. And that's all this old fogy can offer on the word.
Dublin taxi men have given me many interesting words over the years, and only last week a nice man who lives in Tallaght, in thanking me for my usual generous tip, used the word douser, a word I never heard before. It is alive and well in England, it seems, where in the West Country, pronounced doucer, it means a lollipop, and in London town, pronounced as my Dublin friend pronounced it, a fee, a gratuity. The word is from French douceur, sweetness; also, you've guessed it, a tip. Mayhew recorded the interesting compound douceur-man in his Prisons of London (1862); "Douceur-men, who cheat by pretending to get government situations, or provide servants with places, or to tell persons of something to their advantage".
The adjective douce is still to be heard in Donegal. I've heard it pronounced doose. It means kind, pleasant, jolly. The word is common in Scotland as well. Burns wrote of "Ye doose folk I've borne aboon the broo", in The Brigs of Ayr. From the French douse, sweet, pleasant, this.