I would ask them to explain the quote. And then help them understand it.
People repeat it as some mantra. It could have been written in Latin and Old Greek for all that matters, they would not think about it anyway.
Typically it gets started like this:
if (i == 0) faster than
if (0 == i) ?
Bob: don't worry about this, as Knuth said "We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. "
Alice (disappointed and subdued): Oh! Ah yeah I heard about this already. -- don't want to appear too dumb right ?
Carol: I think we should review our algorithm here, O(N!) is pretty bad and won't allow us to scale at all.
Alice: It's okay, Knuth said it: "Premature Optimization is the root of all evil"! -- great sense of accomplishment
This quote is too widespread, I fear, and most of the times provided without any context. It's basically the equivalent to the unfamous RTFM. People get bashed on the head with this, and they don't want to appear dumb since they didn't know about this and everyone seems to, so they shut up and forget to ask why ??.
And then they reuse it themselves, propagating it, and not necessarily in appropriate situations because they have never been given the necessary information to judge whether or not it applied to a particular situation.
It's a vicious circle we are in, since when those cultists reuse it, they cannot provide the context at all, because they never knew it in the first place. But it comes from Knuth, the K in KMP!, the one behind Latex, the one behind "The Art of Computer Programming", so it cannot be wrong... right ?