John Gill Commentary Ecclesiastes 7:6

"For as the crackling of thorns under a pot, so is the laughter of the fool: this also is vanity." — Ecclesiastes 7:6 (ASV)

For as the crackling of thorns under a pot, so [is] the
laughter of the fool
As thorns are weak, useless, and unprofitable; yea, hurtful and pernicious, and only fit for burning; so are foolish and wicked men, (2 Samuel 23:6) (Isaiah 27:4) ; and as the noise and sound of the one under a pot is very short, they make a blaze for a while, and is soon over; so though the laughter of a fool is loud and noisy, it makes no melody, no more than the noise of thorns; and is but for a moment, and will be soon changed for weeping and howling, which will last for ever; see (Job 20:5) ;

this also [is] vanity ;
the carnal mirth of wicked men.