If Job had lied in a business deal, it would violate the eighth commandment (Deuteronomy 5:19). If he lied in court, it would violate the ninth commandment (Deuteronomy 5:20). This sin would deserve judgment of fire (Revelation 21:8).
If Job desired his neighbor's possessions, he would violate the tenth commandment (Deuteronomy 5:21).
then may another eat: This was also speaking against himself (a curse).