The beliefs of his friends (Job 12:3) have caused them to become cold and heartless. Their belief that he deserves his suffering causes them to laugh at him. They do this even though Job (as he continues to remind them) is a righteous and blameless man (see Job 1:1). He used to pray to God and receive answers to his prayers.
4 I am a laughingstock to my friends; I, who called to God and he answered me, a just and blameless man, am a laughingstock.