Also refer to jack off

When Spider-Man rubs his wrist using his hand until a white sticky substance is released, often called, "His Webbing". Spidey often uses this "Webbing" as a form of transportation among other things in order to save the day. This is why when Spider-Man isn't horny, the day does not get saved.

reason my right arm is much bigger than my left

stimulating your penis with your hand to cause orgasm and ejaculation. Male masturbation.

rubbing your boner for insane sexual pleasure
masturbation

Sexually pleasuring yourself either with your hands or a foreign object.