When you hold your hand like spider-man does when he shoots a web so you can use your index finger and pinkie to finger both the pussy and ass hole at the same time.
"The next thing I knew we were both naked and he was spidermaning me, I squirted everywhere!"
"I heard he was spidermaning her and she screamed so loud the neighbors called the cops!"
To do your girl doggy so she cant see you then pull out just before cumming and cum in your hand, call your girls name then unleash your jiz onto her face in the same way spiderman spins a web.
I enjoyed spidermanning your wife last night, she seemed as surpised as you do right now.