Ass crack

[Mark Zuckerberg]

The split between someones ass cheeks.

[Justin Bieber]

The vertical line dividing the left and right ass cheeks.
Crack, and cocaine variants, that were at any point, up someones ass.

[Zipporah Schumaker]

something you should not fall into

[Britney]

the line on your ass that gets erased after sitting down for long periods of time.

[Jason Yan]

The thing you yell when nothing else comes to mind. One of those times when youre so mad that you say something extremely irrelevant and that doesnt even make sense, when you could have just as easily said [ass hole].