When a guy hasn't had sex in a while, and all the sperm that he hasn't cummed, "backs up" into his brain. So now all he thinks about is having sex.

A play on the condition, kernicterus, in which unconjugated bilirubin deposits into the brain of a newborn, causing severe physical and mental problems.
Man, John has a case of spermicterus. All he does is talk about sex. He really needs to get laid.
by rishta September 23, 2011

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