Sorry if you heard before... but here goes
A man and a woman who had never met before, but were both married to other people, found themselves assigned to the same sleeping room on a transcontinental train.

Though initially embarrassed and uneasy over sharing a room, they were both very tired and fell asleep quickly... he in the upper bunk and she in the lower.

At 1:00 AM, the man leaned over and gently woke the woman saying, "Ma'am, I'm sorry to bother you, but would you be willing to reach into the closet to get me a second blanket? I'm awfully cold."

"I have a better idea," she replied. "Just for tonight, let's pretend that we're married."

"Wow! That's a great idea!" he exclaimed.

"Good," she replied. "Get your own f*&^ing blanket."

After a moment of silence, he farted.