1 definition by Bill 

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 spur awkwardness.
We need to double up, tonight. Just make sure we don't look eachother in the eyes.
by Bill  June 12, 2011
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