Sheldon: Whoa. That girl just took a book on geostatistics.
Tam: Yeah, so?
Sheldon: That's not required reading for any science course.
Tam: Maybe she wants to squash a spider with it.
Sheldon: No, look, she's reading it. Who is this mystery woman?
Tam: Should we invite her to have lunch with us?
Sheldon: I don't know. So far, it's just been you and me, and we know that works. Do we really want to mess with success?
Tam: We could think of it as an experiment.
Sheldon: Oh, you do know how to push my buttons.

Principal Petersen: Our next young speaker needs no introduction, but that didn't stop him from writing one and making me read it. [laughter] "Fun fact." [audience groans, murmurs] I hear you. "The word 'valedictorian' is from the Latin 'valedicere,' meaning 'to say farewell.' It is primarily used in the United States, Canada, the Philippines and Armenia." Maybe that fact's more fun in Armenia. Please welcome your valedictorian, Sheldon Cooper.
Mary: Yay, Shelly!
Sheldon: Hello. I'm not very comfortable speaking in front of crowds. But there's a technique to reduce stage fright by focusing on one person in the audience and delivering your speech just to them. That's what I'll be doing today. If it weren't for this person, I wouldn't be here right now. They've taught me a lot, and it's by their example that I found the courage to move forward into this new and exciting chapter of my life. Missy... ...this is for you. Change can be scary, but I know we're going to be fine... ...because like you said, "It's okay to be scared. We just have to do it anyway." So if any of my fellow graduates are nervous about the future, know that you're not alone. I suggest you all try to be as brave as my twin sister. That's my plan. Missy, I wish I could give you advice about middle school, but I was so smart, I skipped it. If you make it to high school, we'll talk. Thank you. [applause]

Sheldon: Missy and I broke a lot of rules the other night, and we've received no punishment.
George Sr.: [sighs] Buddy, it's been a rough week. We're just glad you're both safe.
Sheldon: But in the absence of a divine being, society's rules are what keeps a person's morality in check.
George Sr.: Well, there you go.
Sheldon: No, y-you're not following me. If actions have no repercussions, society breaks down, everything devolves into chaos.
George Sr.: You might be overthinking this.
Sheldon: I thought so, too. Then I thought about it, and I'm not.
George Sr.: Sheldon, you had one bad night. Just let it go.
Sheldon: But... I did something wrong and I got away with it. That's not okay.
George Sr.: Buddy...
Sheldon: Socrates maintained that the man who lies to himself has an enemy living within. He's not even a person. He's just a chaos of selfish desires wrapped in an animal hide.

Missy: What's it like to not believe in God?
Sheldon: It's great. Big fan.
Missy: Are you ever afraid you're wrong?
Sheldon: About religion? Never. About other things? Also never.

Adult Sheldon: As you can see, sometimes a person can be both incredibly intelligent and full of baloney.

Adult Sheldon: Anger is an ugly emotion. Unbridled rage even more so. And when it bubbled up inside me, I channeled it the only way I knew how. I cleaned the house like a man possessed.

Mary: You smoke marijuana?
Sheldon: Mom!
Libby: No, ma'am.
Tam: Just say no. [Mary shoots him an unimpressed look]