(taken from the Danganronpa wikia page) 

Hifumi has a verbose manner of speaking, often going on long-winded tangents about his interests such as anime or fanfiction. He also has a tendency to casually make creepy or perverted comments in the middle of conversations, especially about or to women. He also can't tell the difference between some insults of compliments, as shown when Toko says he smells like a "big fat ugly donkey". He doesn't know if that was an insult of or a compliment. But he also displays some intelligence, showing that he figures out one piece of Sayaka's dying message in the first trial. He also has late reactions to shocking events, as shown when Leon tries to pin the murder of Sayaka Maizono on him, and then again when Chihiro Fujsaki's true gender was exposed. He reacted calmly and interested at first, but then freaks out when he realized the situation.