Sheldon: You have two strikes. Three strikes and you're out. It's a sports metaphor.
Penny: A sports metaphor?
Sheldon: Yes, baseball.
Penny: What was my first strike?
Sheldon: March 18th: you violated my rule about forwarding email humor. You know, the photo of the cat who wants to "has cheezburger?"
Penny: Oh, come on, everybody loves LOLcatz. They're cute, and they can't spell... 'cause they're cats?