Making nylon
When one ejaculates into one's bath water after a nifty tub-wank. The resultant mess of 'man-made' thread like matter is akin to nylon.
I was making nylon in the bath and needed to take a shower afterwards as it clung to my body when I drained the water.
Making nylon
(Verb) Masturbating (male) in the bath.
Wilburrrrrrr! Hurry up out of the bathroom; I want a shower. You'd better not be making nylon in there...