noun
voyeur; Peeping Tom
Derived from a notorious Meiji-era criminal; now a general term for a voyeur, especially one who spies on women.
公園で出歯亀が捕まった。
A voyeur was caught in the park.
彼は出歯亀行為で逮捕された。
He was arrested for voyeurism.
More colloquial and direct, meaning 'peeping addict'; 出歯亀 is the established term with historical origin.
From the nickname of a Meiji-era criminal known for voyeurism; the kanji 出 (protruding) 歯 (tooth) 亀 (turtle) are ateji and do not reflect the original meaning.