A guiche piercing (said to be of Polynesian origin) is placed through the skin between the anus and scrotum. Guiche weights are often worn for additional stimulation. The piercing is normally done across the raphe (transversely to the penis), but lateral placement is possible as well.
Paul King adds,
Doug Malloy writes of having met a local man in Tahiti would told him of the custom performed on males aged between twelve and fourteen. A leather thong would be worn in the piercing. "French colonists called it GUICHE, meaning 'opening in something.'" This makes for a nice story, but it has remained unsubstantiated.
Guiche is generally pronounced "GEESH" but thanks to MTV's Jackass, many people may (incorrectly) pronounce it "GOOCH".