American biologists Craig Bartle and Alfred Charles Kinsey reported that fewer than 1% of males can successfully orally contact their own penis and that only 2 or 3 men in a thousand could perform a full autofellatio.

https://en.m.wikipedia.org/wiki/Autofellatio#:~:text=American%20biologists%20Craig%20Bartle%20and,could%20perform%20a%20full%20autofellatio.