Definition 1: Jack off into the palm of your hand and flick your salty seed like spidermans web, usually onto somebody sleeping
Usage Example: Last night she had a headache went to sleep, so I had a wank and did a spiderman on her face
Definition 2: The act of taking the middle and ring finger together and penetrating the female reproductive area. The pinky and pointer finger are point out(like Spider man shoots his web).
From shnick festun
Usage Example: I just met this girl and i already pulled a spiderman on her