This was a case where imitation was decidedly not the sincerest form of flattery.
It used to be that we said that imitation is the sincerest form of flattery.
They say that imitation is the sincerest form of flattery–but not if you ask John McCain.
If that makes the series sound like a slog, my sincerest apologies.
My sincerest hope is that the film, Betty and Coretta, will encourage all to learn more.
The Christian fervour of the artists led them to give their best and sincerest work to the decoration of them.
The sincerest of women will make no unnecessary confidences to a man.
For Death is near him and Death is the sincerest and most authentic of inspirers.
This can only be done by a writer of feeling, of imagination, and of the sincerest art.
Latterly he took to a teasing process of collaboration, which his sincerest admirers could have willingly spared.
1530s, "pure, unmixed," from Middle French sincere (16c.), from Latin sincerus, of things, "whole, clean, pure, uninjured, unmixed," figuratively "sound, genuine, pure, true, candid, truthful," of uncertain origin. Ground sense seems to be "that which is not falsified." Meaning "free from pretense or falsehood" in English is from 1530s.
There has been a temptation to see the first element as Latin sine "without." But there is no etymological justification for the common story that the word means "without wax" (*sin cerae), which is dismissed out of hand by OED and others, and the stories invented to justify that folk etymology are even less plausible. Watkins has it as originally "of one growth" (i.e. "not hybrid, unmixed"), from PIE *sm-ke-ro-, from *sem- "one" (see same) + root of crescere "to grow" (see crescent).