It could come off as a little snarkier than I would like to be, but as soon as someone says something should have been documented better I ask them where they think I should have put said document. Then I ask them if they looked there before asking me. 9 times out of 10 the answer is no, and it's then obvious to them that if I had already done exactly what they're asking of me, they still would have come and asked me.

Sometimes people have a point and something should be documented better. Especially if I've been asked twice, it's worth documenting better. And I would welcome their input on where and how that should be done. But those are the people are being constructive.