It's an intensification of "what do you want, a cookie
?" which shows lack of interest when someone tells something he considers very cool or amazing, mostly while showing off whith it.
For example, you can use it when you are down and someone thinks he has to tell you just NOW how happy and overjoyed he is.
(I am sad because my love is already assigned)
Annoying person: ...and I just kissed her! She requested me to bring her home and in front of her house she asked whether I wanted to see her stamp collction -haha- and of course I said yes- damn she's so friggin'
hot- and then we went in and she took off her...
You: Hey, do you want a cookie from my shut-up-and-croak-box?