You and your girlfriend are going to be stranded on a desert island today. At first it will be fun because there won't be anything for the two of you to do but have sex on the beach, figure out how to open a coconut, and grow body hair and lose weight.
"If you weren't here, I'd be really sad about this," you'll tell her.
She'll say, "In a lot of ways, being stranded here on this beautiful island with you is like a dream come true. Except in my dream I would probably be able to contact my mother still."
For a little while it will be just the two of you and it will be paradise. Then you'll discover you're not alone on the island. You'll wake up one morning and a man in a dinner jacket and pressed white sailor's pants will be hovering over you.
"Hello," he'll say. "My name is Roberto."
Roberto will have a sexy Spanish accent and he'll explain that when he got stranded on the island a long time ago, the first thing he did was figure out how to press his pants with a warmed strip of tree bark in case a rescue ship ever arrived. He'll also explain that he is very wealthy and that he loves kids.
"I'm breaking up with you," your girlfriend will tell you not four days after having met Roberto. "Back in society it was easy to look past your shortcomings. But here, when the frame of reference is so limited, it's just too easy to compare you to other men, or, I mean, the other man, and realize that I'm getting shortchanged."
Later, Roberto, being the gentleman that he is, will apologize for things having worked out the way they did. And he'll make it clear that even though you three will likely die without ever again seeing another soul but each other, he'll kill you if you ever touch her again.
"You believe I know how to kill a man? I need to know you believe that."
You'll tell him that you believe it. He'll shake your hand and tell you that he hopes you won't let this make the rest of your lives together awkward.
For the next forty years you'll live on the island with your ex-girlfriend and her new boyfriend. Occasionally they'll fight and she'll tell you what a jerk he is, but then they'll make up. You'll help to raise their four children.
Happy The Desert Island Day!