Sheldon: You bought me a present? Why would you do such a thing? I know you think you're being generous, but the foundation of gift giving is reciprocity. You haven't given me a gift, you've given me an obligation. The essence of the custom is that I now have to go out and purchase for you a gift of commensurate value and representing the same perceived level of friendship as that represented by the gift you've given me. Ah, it's no wonder suicide rates skyrocket this time of year. Oh, I brought this on myself by being such an endearing and important part of your life...
I really enjoyed this show when it first began, but I feel the writers are losing their touch. Having said that, I love the following exchange from 'The Gorilla Experiment':
Howard: Hope you don't mind, I told my girlfriend, Bernadette, she can join us for dinner.
Leonard: Sure, the more the merrier.
Sheldon: Wait, no. That's a false equivalency. More does not equal merry. If there was 2000 people in this apartment right now, would we be celebrating? No, we'd be suffocating.