On The Big Bang Theory Season 8 Episode 22, Leonard gives a graduation speech via Skype with the help of Penny, and sports cap and gown that doesn't exactly fit.
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?