I see here several characteristics of the fool when he speaks.
First of all, he speaks out of turn (Ecclesiastes 10:11). He doesn’t need to be prompted to share his futile thoughts or his detrimental words. He just speaks freely to his own hurt and that of others.
Secondly, there is no kindness in his words (Ecclesiastes 10:12). His words will tear people apart before they minister grace to the needy ear.