A Kangaroo Pouch Surprise is when you clasp your penis in one hand while the other hand is in the shape of the middle finger gesture. The middle finger pushes down on the head of the penis, causing it to go inside the penile shaft, forming a baggy of skin. Very quickly the middle finger hand pinches off the skin, creating a "kangaroo like pouch". You then proceed to urinate, thus filling up the pouch. When you release your fingers, the urine filled pouch bursts everywhere creating a "surprise" of urine.
Cooper wanted to impress Beth by showing her that he can successfully perform a kangaroo pouch surprise on her stomach.
by Jrrywbb May 12, 2016