Make her pregnant.

Seriously? What a bitch -.-

Well if she thinks that's acceptable it's probably a good thing she was faking it because she's nowhere near mature enough to be a mother.

She and her friends have a pretty warped sense of humor. Let's just hope any future (real) children don't inherit that particular trait.

I'm sure she wants to have a real baby with you. This was just a trial run to see how you might be as an expectant dad. I'm sure you passed with flying colors because you're a great person!

That is so messed up. If I were you, I would have a hard time trusting anything she says.

pretend that you don't know, have unprotected sex and tell her that anyway she can't get pregnant twice

While it was a bad joke try to put this in the past. She was just trying to have fun with the girls, odd fun but none the less. Tell her that's not something to joke about and leave it alone. The guilt will get her and serve its own justice if you react in a mature way.

She has a weird sense of humour.

op, it sounds like you need to have a serious talk with your wife. try to make her understand the difference between a harmless joke and emotionally crushing her husband. she may have seen the whole ordeal as hilarious, but you should explain to her why it is not. when she realizes her error, move on from this and mature together before really having a child.