Two people turning their backsides closely against each other and pooping, causing the feces to be "pressed like a pancake" inbetween the two bodies. Usually done in sexual euphoria.
Derek hooked up with a girl at Panini's last night. He said it was the time of his life because after intercourse she wanted to do the pancake press. He was skeptical at first. But now all he does is do a solo press against the mirror.