હસવું ને હાણ.

hasavuṁ nē hāṇa.

Literally: Laughter and ruin.
What it means: Foolish mockery or unserious behavior often results in grave harm.

Also said as

ગુજરાતી કહેવતસંગ્રહ (Gujarati Kahevat Sangrah) (1921) · read from the scan by machine — the Gujarati itself is unchecked · English is machine-made and nobody has checked it yet

Heard it differently, or know we've got the sense wrong? Tell us — that is exactly the kind of correction this needs.