Not sure if I addressed this point in class, but I remember one point in chapter two where the underground man talks about magnanimity, which is a "benevolence" or forgiveness given to those such as a rival or below one's own power, mental or physical. He says that magnanimity is useless even if he possessed it. I just want to explain his potential reasoning here. Consider also that he himself consciously regards both his situation and himself as "hopeless". Add this to how he claims to take offense as a humpback or dwarf (meaning that he often would take offense and be hopeless to combat such ridicule) and we can wholly understand that he considers his hopelessness a sort of disability that would compel him to forgive others (if he had the sensitivity to do it) in such cases as feeling ashamed for being cleverer than those around him. So even he essentially takes a strength of his, his so proclaimed cleverness, and because he has no magnanimity, due to the fact that he feels hopeless, he feels ashamed.
So if I wasn't clear, which I don't think I entirely was, the reasoning behind his opinion that his non-existent magnanimity is useless was that he is not in a position to forgive but instead feels himself in the position to be forgiven, because he feels his hopelessness draws ridicule to himself.
In the process, that explains why he feels ashamed to be cleverer than others around him, because he both feels undermined by his hopelessness and feels that he is still in no position to forgive others "below" him because of that.
Kind of disturbing now that I think of it. Just how psychologically trapped this man feels. (I'm not sympathizing.)