The guys gather round Leonard as he sits in his time machine which arrive. The time machine is, of course, the prop from the 1960 movie that he bought off ebay.
Looks like Sheldon, Raj and Wolowitz were clearly too busy for their group dinner date with Penny. They have important things to do... like play Jenga!
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?