Funnyman Ricky Gervais has been left scarred for life by the sight of his pal Louis C.K. naked.

The U.S. comedian stripped down in front of the Brit for a medical scene in his comedy series Louis and Gervais can't get the image of his pal's genitals out of his head.

He recalls, "It was horrendous... I was this crazy doctor who had to give him a rectal examination and it was horrible... He just took his trousers down and he'd sort of hidden that (penis) with some sort of cellotape thing... which made it look worse... It looked like offal in an old bag that was thrown away.

"It was disgusting... He was hot and clammy and I had to go up there... and I could smell everything... Sweat and shame... (He has skin) like an undercooked chicken."