: Penny’s ex-boyfriend Zack and his wife Marissa ask Leonard to be their sperm donor because Zack is infertile.
: Although Penny initially said she was fine with it, she begins to have second thoughts. To prevent the donation—which requires Leonard to abstain from sex—she attempts to seduce him. [S12E15] The Donation Oscillation
: Ultimately, Leonard decides not to go through with it. He realizes he would be heartbroken to have a child in the world that he couldn't personally father. The "Vomit Comet" : Penny’s ex-boyfriend Zack and his wife Marissa