"He just popped a cap in it."

Proper Inflection: "Pop a cap in it!" ("it" is usually referring to "yo ass")

Talking about a recent visit to the dentist, I overheard a girl say that she needed to have a broken filling fixed. After determining that another filling probably wouldn't last long, the doctor made an alternate choice. She summed up the story by saying, "So, he just popped a cap in it."

Example of intended use:
So you'd better grab a gat and pop a cap in they black ass
And let loose the whole clip
And let these motherfuckers know that you ain't taking no shit.
-"Get In Where You Fit In", Too Short