Police in Chandler, Arizona said 27-year-old Joshua Seto and his fiancee, Cara Christopher, were walking towards a grocery store when the shooting happened last week.
The pink gun, which was pushed into the front waistband of Seto's pants, fired, striking his penis and continuing through his left thigh, The Arizona Republic newspaper reported.
Ms Christopher called the emergency services, telling a 911 operator: "He's still coherent and everything but he's bleeding quite a lot. He is still conscious, there is just a lot of blood."
The operator told her to apply direct pressure to the wound with a dry towel or T-shirt, but not to look at it.
Ms Christopher replied: "I did look at it. It's pretty bad."
Chandler Police Detective Seth Tyler told Arizona residents to use holsters, not waistbands, to carry their guns, adding films and television shows like Sons of Anarchy, which show tough men shoving guns into their jeans, were not realistic, the Republic reported.
"Whenever you handle a firearm, whether you are a novice or experienced, always treat firearms as though they are loaded," he said.
"If you are going to carry a handgun on your person, use a holster, not your waistband."
Detective Tyler was unsure of the type of gun, or whether it had a safety that was off.
He also says it's unclear if Seto has been released from the hospital or suffered any permanent damage.
smh.com.au with AP