Outcast boy meets girl underwater

This is The Country of the Kind by Damon Knight.

The story is set in a future world in which violence and crime have been almost entirely eradicated. The main character is a man who is capable of antisocial behavior and who considers himself “the king of the world.” He is allowed to do what he wishes, take what he wants and go where he pleases without reprisal, so long as he does no violence to another human being. The “humane, permissive” society in which he lives has adopted a threefold solution for someone who is, by their standards, insane. The first is excommunication - no one is to interact with him or even acknowledge his existence, other than by the apparent worldwide directive identifying him and calling for this punishment. Secondly, he is thrown into an epileptic seizure whenever he attempts to commit violence against another human. Thirdly, his body and waste give off a highly offensive odor, undetectable by him, to identify him, warn others of his presence and drive them away.

The story ends with a desperate plea from the protagonist for someone, anyone to join him in his rebellion against what he perceives to be a wholly passive society, which has lost any spark of creativity or will to achieve greatness.

The story links violence to artistic expression. The protagonist "invents" drawing and sculpture, only later realizing, from old books, that these things had existed in the past, and notes that all great artists had lived in especially violent times.