This Victorian phrase means 'don't lie to me'. In the 1800's, it was common for dog salespeople to try to pass mutts off as pedigrees. This is supposedly the origin of the phrase (which was popular until the 1870's).
“You think I'd believe that you're a wizard who's also the cousin of royalty and Bill Gates' twin brother? Don't sell me a dog.”
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. Penguin Books,1992. p. 38)