In a game where every possible outcome could result in an agreed monetary win, the process of "doubling up" takes hold. In a game where the winnings is double the place, the idea is to start with low bets, and always pick the same outcome. Should you lose, double your last bet and place for the same outcome. Repeat this until you have won. Comparing your total winnings to your total place, you will have gained one unit.
Of course, there is no garuantee that your wallet can withstand the number of losses needed to recouperate your loss.
In sleepovers, it's the act of having to sleep next to someone of the same gender in the same bed.
The term doubling up is commonly used to make the one using the word seem less of a homosexual, as saying "Let's sleep togeether." Can spurawkwardness.