Fiestas
I know this has been mentioned a bunch of times already, but when she (I think it was Sue Bob, if I'm not mistaken) asks for the fajitas, and the guy on the drive-thru speaker says they don't have fajitas, she questions- "You don't have fiestas?". I absolutely *beep* lose my mind every single time I hear that. Kills me. *beep* slays me.
I hope everyone else got such a good kick out of that part as I did.