(ordering at the Cheesecake factory)
Priya: I'll have the shepherd's pie. Leonard, do you want to split it with me?
Penny: No, no…
Priya: Why not?
Penny: You know, milk in the taters, milk in the gravy, Parmesan crust, your lactose intolerant boyfriend will turn into a gas-filled Macy's day balloon! (everyone laughs)
Sheldon: Not quite accurate. Macy's day balloons are filled with helium, whereas Leonard produces large amounts of methane. (everyone laughs, then Sheldon joins in)