When a person fills their anal cavity with lube, corn syrup, and black dye, and surprises someone with it. Usually a significant other during sex.
Jimmy was shocked when he saw Susan gave him Cthulhu's Sticky Surprise after only the second date.
The act of retaining a concoction of corn syrup and black food coloring in one's rectum moments or sometimes hours before performing anal sex; terrifying the penetrator.
Yeah, my girlfriend is way too devoted to Halloween, man. She even pulled Cthulhu's Sticky Surprise on me. I had ants in my apartment for weeks.