A man and a woman who have never met before find themselves in the same
sleeping carriage of a train.  After the initial embarrassment, they
both manage to get to sleep; the woman on the top bunk, the man on the
lower.

In the middle of the night the woman leans over and says, "I'm sorry
to bother you, but I'm awfully cold and I was wondering if you could
possibly pass me another blanket."

The man leans out and, with a glint in his eye, says, "I've got a
better idea... let's pretend we're married."

"Why not," giggles the woman.

"Good," he replies.  "Get your own damn blanket."