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.
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?
Cookie boxers is when your boss tricks you by telling you that he has brought in cookies and they are in the restroom. He is then there stood naked and gives you the opportunity to do the dirty in the office you’ve always wanted
i was walking into the lockerroom to get my sportsgear when i saw my girlfriend giving head to a teacher while taking it in the ass by the principle so i mummbled "You Jibbering Box A-Cookies" and backhanded that bitch in the face.