It's a more sophisticated way of saying "alcohol jacket." Saying that you're wearing an alcohol jacket makes you seem a little less classy. Not only is saying you're wearing a hypothetical coat more entertaining, it's also a little less obvious.
After a night of drinking:
Guy 1: "Man! It's so cold out here. I can't believe we're drunk and walking home in the snow!"
Guy 2: "I know!"
Guy 1: 'Hey, aren't you cold in just a t-shirt?"
Guy 2: "No way man! I'm wearing my hypothetical coat!"
The frothy mixture of semen and saliva that results from pushing someone's cheeks together after having received ejaculate in the mouth and not swallowing.