The state of one who, with their mind in the gutter, unintentionally has given themselves a powerful erection that, upon lack of release and subsequent contraction, shriek in agonizing pain in the state known as "blue balls".
A state of blue balls with an origin rooted in fantasy.
I was thinking about Trish's ass in Calculus and I got the worst Gutterballs I've ever had in my life.
The state one experiences when their mind is roaming, or "in the gutter", which results in a subsequent erection. The lack of release results in Blue Balls, ergo, Gutterballs.