Sheldon: 1234 is not a secure password.
Store Clerk: You don't work here.
Sheldon: Well aparently no one does.
Sheldon: What type of Computer do you have? And please don't say a white one.
[Sheldon is refusing to buy a present for Leonard]
Howard: [to Penny] Try telling him it's a non optional social convention.
Penny: What?
Howard: Just do it!
Penny: [to Sheldon] It's a non optional social convention.
Sheldon: Oh! Fair enough.
[Penny surprised]
Howard: He came with a manual.