What are yours?
Here are some favorites that I can think of at the moment:
Seto Kaiba to Jou: "Me? Duel you? I'd have more of a challenge playing solitaire."
Jou: "Just put it on my tab, Gramps."
Solomon Moto: "Your tab's past due, Joey."
Jou: "Then put it on Tristan's."
Seto Kaiba: "It's the latest state-of-the-art system that recreates the virtual dueling arena setting anywhere."
Jou: "Looks like a regular old briefcase to me."
Seto Kaiba: "It's in the briefcase, you moron."
Mokuba: "I asked Yugi and his friends for help."
Seto: "You did what? You know how I feel about Yugi!"
Mokuba: "But who else was I supposed to turn to?"
Seto: "Anyone else!"