Mondo's wikipedia page: https://danganronpa.fandom.com/wiki/Mondo_Owada

As according to the wiki, "Behaving like a stereotypical delinquent, Mondo is foul-mouthed and can come off as a rude and an intimidating individual. When Makoto first met Mondo he did his best to keep the conversation short, as he realized Mondo could become easily aggravated depending on what was said. He is very easy to provoke, and will not hesitate to resort to violence if he starts to lose his patience. This is shown during his interactions with Byakuya who acts condescendingly towards him, prompting Mondo to fight back without considering the consequences.

Just like Chihiro, Mondo has a severe complex about being seen as weak, which he represses by constantly repeating in his mind that he is strong. This complex stems from the fact that his gang members tended to look down on him due to his status as the little brother of Daiya, the first leader of The Crazy Diamonds. Mondo ultimately caused his brothers death in a street race by acting rash in oncoming traffic, prompting Daiya to save Mondo in exchange for his own life. It was Mondo's own weakness who caused Daiya's death and this constant burden was placed on him, as he had to live with and share the lie with the rest of his members that it was Daiya who had acted rashly."