The word Cumpiss is a combination of the words, "cum" and "piss". As the name suggests, it refers to the process of urinating after ejaculation. Peeing after ejaculating often causes your urine to become more viscous - almost of sticky and thick consistency and may be a bit harder to control at times.
It wasn't just an ordinary piss, it was a cumpiss
"Hey bro where, were you"
"oh sorry bro just taking a cumpiss
The act of post-sexual activity, after engaging in an orgasm, and forgetting what happened before the nocturnal emission, and/ or ejaculation, occurred.
Person 1: So I was fucking my wife, right? And then we stopped, and I wanted left overs for dinner, but forgot what we had! Damn Cumnesia.