Ibn Ezra: His friend mocks him.

Devar Eliyahu: Those who succeed, they mock me.

Malbim: Tzufar said "Mi Yiten Eloka v'Yaged Lecha Ta'alumos Chochmah" (11:6). If you would call to Hashem, He would tell you that perceived man is not man himself. Even if he appears to be a Tzadik, perhaps he is a Rasha. You do not know yourself! Iyov answers, this is a joke. One who knows that he is a Tzadik, should he consider himself a [Safek] Rasha?! Also saying that man has choice even though Hashem knows what he will choose, is a joke.

Rashi: He will cry amidst pain from your vexing him.

Ibn Ezra: This is astounding - he mocks his friend, and Hashem answers him?!

Devar Eliyahu: This is a parable - it is as if they call to Hashem and He answers them, i.e. He gives a big influence to them - they have a pure Tzadik to mock him.

Rashi: This is what Hashem answers the Tzadik [who is the victim of their words] - refer to 12:5:1:1.

Devar Eliyahu: Refer to 12:4:2:3.