Do not try to please everybody. Try to please God, the angels, and the saints–they are your public.Attr. St. John Vianney
I was perfectly willing to believe this quotation is authentic, right up until I hit the phrase after the dash. I have a hard time thinking that St. John Vianney would think in terms of having a “public.”
The earliest English citation for “public” in this sense in the OED is 1823. Since the Curé died in 1859, his life does overlap the time when this sense was in use, but (a) he spoke French and (b) I don’t think he would have picked up a colloquial English phrase like this. So either it’s a translation of an equivalent French phrase (I have no idea what that would be) or it’s very likely a fauxtation.
Since “public” is the word whose authenticity I find suspect, it’s a handy search term when searching through the works of the saint and works about him. None of the hits in Abbé Trochu’s biography match. Nor does the one hit in the Little Catechism. Nor does it show up in any of the other works searchable on Google Books. Nor is it in the Thoughts of the Curé of Ars (1859 edition). I also tried works by and about him at the Internet Archive, also without success.
My general Google search turned up tons of hits, none with citations. Searching Google Books especially, the oldest hit for the full quotation is from Saintly Solutions to Life’s Common Problems, by Joseph M. Esper. I’ve encountered this work before in investigating quotations, and he doesn’t cite his sources.
I then started to wonder if I could find the first part of the alleged quotation in the saint’s works. The short answer is no.
My verdict is that the first portion of the “quotation” is plausible but uncertain, and the part after the dash is almost certainly not from the saint.