Is the phrase "What is this lack of ادب (respect/manners)?" considered a curse word that would cause a divorce to occur, based on a previous oath that divorce would occur upon cursing again?

If the word spoken was not intended as an insult, then nothing (no consequence) follows from it. However, if it was intended as an insult, then divorce occurs according to the majority of jurists. Some scholars are of the view that an expiation for breaking an oath is required if divorce was not intended, but rather a threat; however, the opinion of the majority is the one acted upon.

The wife should know her husband's rights and not overstep her bounds or insult him. The husband should resolve problems through means other than divorce to avoid its negative effects. When angry, it is preferable to distance oneself until tempers cool.