Stephen Hawking: You made an arithmetic mistake on page two. It was quite a boner.
Sheldon: No, no ... that can't be right. I-I don't make arithmetic mistakes.
Stephen Hawking: Are you saying I do?
Sheldon: Oh, no, no, no, of course not. It's just, I was thinking.... Oh, gosh, golly, I made a boo-boo and I gave it to Stephen Hawking.
Stephen Hawking: Great, another fainter.

Sheldon: Professor Hawking, it's an honor and a privilege to meet you, sir.
Stephen Hawking: I know.

Howard: No ... about my job. I want you to tell me I'm good at what I do.
Sheldon: You're obviously good at what you do.
Howard: Well, then why are you always ripping on me?
Sheldon: Oh, I understand the confusion. I have never said that you are not good at what you do, it's just that what you do is not worth doing.

Howard's mother: It's this dress. When I put my front in, my back pops out. When I put my back in, my front pops out. It's like trying to keep two dogs in a bathtub.
Sheldon: What do you want me to do?
Howard's mother: We're going to have to work as a team. Get in here, grab a handful and start stuffing.

Sheldon doesn't know when he's being mean because the part of his brain that should know is getting a wedgie from the rest of his brain

Bernadette

Bernadette: You're being mean to him.
Howard: He's mean to me all the time. You've heard him tease me about not having a doctorate.
Bernadette: If you don't want to get teased about that, get a doctorate. I have one; they're great.

Sheldon: You don't think I'm condescending, do you?
Penny: Well....
Sheldon: Oh, I'm sorry. Condescending means....
Penny: I know what it means. And yes, you like to correcting people and putting them down.
Sheldon: Au Contraire. When I correct people I am raising them up. You should know, I do it for you more than anyone.

Penny: I know, he's the wheelchair dude who invented time.
Sheldon: That's close enough.

What are you all staring at? You ever seen a man try to get a meeting with Stephen Hawking before?"

Sheldon [in a French maid costume]

You make sissy on your belt buckles? Mee-Maw's forks never had that.

Sheldon

Sheldon: That's a lot of belt buckles.
Howard: Funny thing is, I only have one belt.

Howard: Let me try gangsta: Hells naw.

The Big Bang Theory Season 5 Episode 21 Quotes

That's amazing. You'll be like his pit crew.

Leonard

Howard: So, I got the craziest email this morning.
Raj: I hate to burst your bubble, dude, but those penile enlargement pills do not work.
Howard: Believe me I know.