An alcoholic beverage you drink in the shower. If it's alcoholic and you're drinking it in the shower, you're drinking showcohol.
Jake: "You wanna see 'Hanna' in theaters tonight?"
Nicole: "EW! No, what? No, gross, oh, no, what? No way, man."
Jake: "How about we just have a showcoholic beverage instead?"
Nicole: "Oh yeah, I love showcohol!"
Jake: "I'll bring the wine, you pre-heat the shower?"