The man was arrested for indecent exposure in the park, and the police confirmed he was an exhibitionist.

exhibitionist 是由名词 exhibition（展览、展示）加上后缀 -ist（表示"从事某种行为的人"）构成的名词，字面意思是"喜欢展示自己的人"，特指"有暴露癖的人"，即通过公开暴露自己身体来获得快感的人。