He was arrested for sexual assault on men

Puri-Puri Prisoner is a flamboyant, openly homosexual superhero. He takes an interest in other good looking male heroes and criminals; an interest which led to his titular jail sentence, as he kept attacking them. Criminals that he apprehends are then added to his harem. He appears to be rather absent-minded, as he did not think to remove his sweater before bulking up, and then blamed his opponent, the Deep Sea King, for its destruction.

The word Puri-puri describes the feeling of snapping into a fresh shrimp or a plump hot dog. Bursting with juiciness and bounce, puri-puri evokes the springiness and slight resistance of collagen—which is why it’s also sometimes used to describe a young girl’s cheeks.

(Source: One Punch Man Wiki)