fapcabin

When a sheet is hung from the upper bed on a bunk bed, the lower bed is obscured by the sheet, thus creating a fapcabin.

Ben- "What are you doing?"
Ryan- "Hanging a sheet from your top bunk bed."
Ben- " Ohh okay. So you're making a fapcabin!"

Later that night-
Ryan- *fapfapfapfapfapfap*