Penny: Leonard Hofstadler...
Leonard: Yes?
Penny: Will you be my valentine?
Leonard: Sorry. Maybe next year. I'm just kidding! Romance ninja. Let's have sex.

Leonard: Penny, as a scientist, my job is to figure out why things happen. But I don't think I'll ever understand how someone like me could get to be with someone like you. You know maybe I don't need to understand it, I just need to be grateful. I love you, Penny.

Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis?
Sheldon: Screwed?
Leonard: There you go.

Leonard: My point is, while you're spending all this time on your own, building computers or practicing your cello, what you're really doing is becoming interesting. When people finally do notice you, they're gonna find someone a lot cooler than they thought. And for those of you that were popular in high school, it's over, sorry. Thank you. Congratulations.

Howard: She hid my XBOX like I'm a child. And my mom got me that for my birthday so if you don't give it back, I'm telling.

Bernadette: If you like pushing buttons so much, try pushing them on the washing machine.

Howard: A micro-valentine for a microbiologist.
Leonard: From her micro-husband.