Jon: Can ya put that out?
Don: I'm holding it out the window and blowing the smoke outside!
J: It's blowing back into the car.
D: A little smoke won't hurt ya.
J: Wrong, man. It's got nuclear radiation in it.
D: Cigarette smoke? J: Yup!
Q: Why ''yup'', not 'yes'?
ANSWER: We use the "yup" instead of 'yes' to be casually clever or sarcastic:
"You're good at math!" said Jack, flirting a little.
"Yup!" replied Jane with a smile, as she turned to go.