In nine seasons of The Big Bang Theory, we've never met Leonard's father. Until now! Chaos ensues when he shows up, along with both Leonard's other and Sheldon's.
Sheldon: I'll have a diet Coke. Penny: Can you please order a cocktail? I need to practice mixing drinks. Sheldon: Fine... I'll have a virgin Cuba Libre. Penny: That's... rum and Coke without the rum. Sheldon: Yes, and would you make it diet?