Diamonds on my neck call it the ghetto's guillotine

from Rick Ross – High Definition Lyrics on Rap Genius

Meaning

Probably Rick Ross' most Jay-Z esque line ever…A guillotine is this.

Basically you put your neck in the hole and it decapitates you. The Bawse is saying that people strive for the diamonds, which we wear around our necks, and in pursuit of that we go so far that we die for it.
We go for the diamonds and we die for it. It takes our head in two ways. We wear it around our heads and we die for it (aka lose our heads which is death).

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