To tell someone to use their imagination. In effect, most people, at least normal, non-homoerotic sadists, wouldn't know what a split cock looks like, so they'd have to use their imagination.
"Hey Jimmy, I heard that there's going to be a comic book about gay school children trapped in Hell, what do you think that'll be like?"
"Splitcock."
"What?"
"Use your imagination fucktard."
"Splitcock."
"What?"
"Use your imagination fucktard."
by Razor Jones November 25, 2006