(Howard has just told Mary about his upcoming trip to the International Space Station.)
Mary Cooper: I bet your mom is really proud of you.
Howard: Nope. She says if I don't back out, she's gonna go on a hunger strike. It'd take years before she'd be in any kind of danger, but still.

Howard: Sheldon, if you were a robot and I knew and you didn't, would you want me to tell you?
Sheldon: That depends. When I learn that I'm a robot, will I be able to handle it?
Howard: Maybe, although the history of science fiction is not on your side.

Bernadette: You can't just throw everything in the closet.
Howard: Hey, you can tell me what to do and how to do it, but not both at the same time. This isn't sex.

Stuart: I'm not bringing your mother. I have a date.
Howard: Oh, so now you're cheating on my mother.

Leonard: Howard, this is big science. You could be the engineer who builds the equipment that puts us on the cover of magazines.
Howard: I could also be the engineer who builds the crossbow that kills Sheldon.

Leonard: What would you guys do if you were me?
Wolowitz: I would take Sheldon to Switzerland.
Leonard: Seriously?
Wolowitz: Absolutely. And I'd leave him there.

Wolowitz: I'm a horny engineer, Leonard. I never joke about math or sex.

Howard: Hey, you want to make sure he gets nowhere with Penny without jeopardizing your friendship with either of them?
Leonard: I'm listening.
Howard: Just tell him to do everything you've done with her for the last two years.

Howard: On the potty, what are you five?
Raj: It's a potty, what do you call it?
Howard: A toilet.
Raj: That's a little vulgar for the dinner table, don't you think?
Howard: And potty is okay?
Raj: Potty is innocent. Potty is adorable.
Howard: What do you do on the potty, wee-wee?
Raj: If I don't have to boom-boom.

Sheldon: Aren't you gonna come with me?
Howard: While you confront your mother about her sex life? I'd rather go back to that bar in assless chaps.

Howard: How are the taxes going?
Bernadette: Okay, but you've got a lot of receipts for the Lego store in here.
Howard: Those are business expenses. You can write those off.
Bernadette: A $200 R2-D2 is a business expense?
Howard: Oh, Bernie, you're gonna have to sound a lot more confident when we get audited.

Howard: Try telling him it's a non-optional social convention.
Penny: What?
Howard: Just do it!
Penny: It's a non-optional social convention.
Sheldon: Oh, fair enough.
Howard: He came with a manual.

(Sheldon smiles in a grotesque way).
Howard: Oh crap that's terrifying.

Raj: What do you say, Howard?
Howard: I say Vegas baby!
Raj: What are you gonna tell your mother?
Howard: Sea World baby!

Wolowitz: That's more like we're a tall thin woman who wants to make a coat out of your Dalmatians.