I have seen and participated in this elsewhere, so I (sort of) recuse myself. Regardless, the game is inspired by the ability to add "in bed" to any fortune cookie fortune, and make it grammatical. Here, we will take movie titles, and add "...between your legs" to them, preferably resulting in some purile double-entendre.
Some examples to get the ball rolling:
Harry Potter and the Goblet of Fire between your legs
First Blood between your legs
Lemony Snickett's A Series of Unfortunate Events between your legs
Et cetera. Et cetera. Et cetera.
Have at it.