When you need to use the restroom, are still thirsty, and just happen to have a drink in your hand. As one liquid goes out, the other is taken in, hence the "Swap". Many individuals try to consume their entire beverage before they are finished urinating.
"Oh man, that party was insane, people were so drunk that they were even Omaha Swapping it out in the bathrooms."
by Big Daddy Phil June 24, 2008