Masturbation
True, God does not say in the Bible, "Thou shall not masturbate", therefore it's not a sin. Masturbation feels good and is pleasurable, and can relieve stress. God did not intend for human beings to forgo all pleasures in life and to be stressed out all the time. It's a perfectly natural act, and in men, it has been shown that if done regularly, the chance of getting prostate cancer is greatly reduced.