Sheldon: Penny, if I'm going to get Leonard a gift, I'm going to do it right. I refuse to let him experience the same childhood trauma I did.
Penny: I know I'm gonna regret this, but what trauma?
Sheldon: On my 12th birthday, I really wanted a titanium centrifuge so, you know, I could separate radioactive isotopes.
Penny: Of course, yeah.
Sheldon: Instead of a titanium centrifuge, my parents bought me-- Wow, this is hard. They got me a motorized dirt bike.
Sheldon: What 12-year-old boy wants a motorized dirt bike?
Penny: All of them.