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.

Sheldon: I see. I assume since the rest of you have set the bar so low, you're saving the most impressive contribution for last. Go on Howard, dazzle me.
Howard: Well, my power is the ability to pretend like I give a damn about your piddly-ass problem. And that's 24/7 buddy.

(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.

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.

Sheldon: You shot your spit in my mouth!
Howard: Is that gonna be on the test? Because I don't think I can do that again.

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.

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

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.

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

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

Rajesh: Missy. Do you enjoy pajamas?
Missy: I guess.
Rajesh: Yes, well, we Indians invented them. You're welcome.
Howard: Yeah, well my people invented circumcision. You're welcome.

Raj: Are they actually arguing about comic books?
Leonard: No, that can't be right.
Howard: Maybe "Thor's Hammer" is a new color of nail polish.

Bernadette: I'm excited to meet Emily.
Howard: I just hope he doesn't blow it.
Bernadette: Why would you say that?
Howard: Because he's Raj. That's his thing. Beckham can bend it. Ralph can wreck it. Raj can blow it.