The act of urination in another's anal cavity. Although completely absurd, it is erotic in the most fecal kind of way. Apparently the piss running through and out of one's asshole is a sensation only one who is in touch with all five senses could fathom.
1.)"Christina gave Stephen a wet cushion, what the fuck?"
2.)"Josh wet cushioned that bitch last night."
3.)Justin was completely turned on, after explaining the act of the infamous "wet cushion" to Katie, they proceeded in doing the ungrateful yet exotic act of sexual pleasure.