Sometimes used in lingo associated with African American gangs, cooler often means the stomach or abdominal area. Just as the grill means mouth, the cooler means stomach.
"I got into a fight and that asshole punched me in my cooler, bruh!"
In N.W.A.'s hit, "Dopeman" the following line was used:
"Yo, Mr. Dopeman, you think you're slick
Ya sold crack to my sister and now she's sick
But if she happens to die because of your drug
I'm puttin' in your cooler, a .38 slug!"