Michael Carney, 41, claimed he was too embarrassed about the size of his manhood to expose himself to women and showed the court photographs as proof.
But the jury at Teesside Crown Court convicted the father-of-two, of Stockton, Teesside of seven counts of outraging public decency.
The jury was then told he was earlier found guilty of five sexual assaults.
'Smaller than average'
Carney, of Fleetham Grove, will be sentenced for the flashing and sex assaults next year.
During the three-day trial the defendant told the court: "It causes embarrassment to myself, even to the point where it is with my wife. I wouldn't want myself to be seen in public like that.
"My genitalia are underdeveloped and it is so much smaller than average."
He showed the jury photographs taken by his wife to prove his claims.
But the jury convicted him of flashing in front of six different women over a number of years.
The court heard that on most occasions, he exposed himself to passers-by while standing naked in the front window of his home.
But he was also spotted naked on the driveway of his home.
The court also heard he had already been convicted of sexually assaulting five females in his local area while out jogging.
Judge Brian Forster told Carney he was likely to receive a jail sentence, before granting the quality inspector for a plastics firm bail.