In Job 6:25-29, Job earlier challenges his friends' reproof as not upright — directly parallel to calling them 'vain' here.

Job 13:4-9 accuses them of whitewashing with lies and being worthless physicians — the same vain talk condemned here.

Job 16:3 calls their words 'windy words' — a direct parallel to the vanity Job sees in them here.

Job 19:2 complains they 'break me in pieces with words' — the same vain, tormenting speech Job condemns here.

Job 21:28-30 presents evidence that the wicked prosper — the very thing Job says his friends have seen but ignore, making them vain.

Job 26:2-4 sarcastically mocks Bildad's useless counsel — directly parallel to the vain words Job condemns here.