When you want to piss but the damn pee won't come out! Possibly because your urethra is jammed with cum, pussy juice, coke, whatever
Etymology: verb form of constapiss, which is cheaply and crudely derived from the term constipate
Adam: I nearly blew my balls out when I tried to take a piss... I was constipissing!
Lilith: Have you been jamming blow up your urethra again?!
Adam (meekly): yes :(