Top Definition
The substance in between a man's ass cheeks that creates skid marks. Also known as butt butter, gack in the crack is usually formed as a result of several components put together. These are:
1) A hairy ass
2) A moist defecation followed by clean up with cheap TP
3) Physical exertion that causes the hairy ass to perspire
Mike took a hurried dump in the portajohn outside the stadium and then went back to tailgating. It was a long walk back to the pickup and the hot weather made him sweat. By the time he got back to the beer cooler he had some gack in the crack.
by Wiseman July 14, 2006

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