In a younger and more diverse group of men, we see that unsolicited dick pics are linked to narcissism; however, in an older and Whiter sample of men, we see unsolicited dick pics linked to low self-esteem instead.
In two studies of adult men, 41-48% admitted to having sent at least one unsolicited photo of their penis to someone. Most were sent with the hope that the recipient would send a nude in return; however, some men had other motives.
The Psychology of Unsolicited Dick Pics: How Many Men Have Sent Them, and Why?