You and the lads each buy individual electric fly swatters, sit in chairs, then place the electric fly swatters over your genitals. One of you then puts pornography on a phone or larger screen for all to view. The goal is to not get an erection, to therefore not get an electrocuted penis.
Having just relieved yourself in your hand; the act of then throwing your spunk across the room in the exact motion that Spiderman would release a web from his wrist.
Rob: 'I'm going out with this slaggy girl, she loves it when I Spiders web in her face'