Pleasure's a sin, and sometimes Sin's a pleasure.' - taken from -

Several other quotes from Don Juan by Lord Byron - (Oxford References)
Sweet is revenge—especially to women.
Don Juan (1819–24) canto 1, st. 124

Pleasure's a sin, and sometimes sin's a pleasure.
Don Juan (1819–24) canto 1, st. 133

Man's love is of man's life a thing apart,
'Tis woman's whole existence.
Don Juan (1819–24) canto 1, st. 194