Very, very sticky weed. As coined by T.I. in the classic "Rubberband Man" in the line

"Herb so sticky it stick to the walls like Spiderman"

When a girl is going down on you, and just before you climax you pull out of her mouth and nut in your own hand. Then fling the jism in her face, as you jump to your feet, making sure to properly mimic Spidey's web slinging hand motions. Now stand in a position of bravery, and power like any superhero would. Be sure not to react when she yells at you. Stand tall and proud, not too many guys get the chance to do that these days.

ive nothing much to add to the whole cumming in your hand and flinging it in her face except when you do you have to yell "go web go!"

hes a superhero you pervs!!

When you are banging a chick from behind, you cum in your hand and spit on her anus, thus making her think you have ejaculated on her, when she turns around you throw that shit at her in a spiderman-esque fashion.

This guy who does whatever a spider can.

A Spiderman is when a guy cums in his hand then flings it onto his partner's face just like Spiderman shoots his web. (Original)

When dancing with a girl at a frat/bar you place your hand down the front of her jeans and slide in Spiderman fashion (middle and ring finger inserted with other three fingers out to the sides a la Tobey Maguire). Singing the Spiderman theme song adds to the ambiance.