A catchphrase uttered by members of a rap label named G-Unit which is headed by rapper 50 cent. The catchphrase is often recited in an aggressive manner with an emphasis being placed on the 'NIT' of word 'Unit' towards the end. It is supposed to convey a don't-mess-with-us-coz-I'm-a-gangsta attitude. Supposed to. The rapper known as 'The Game' might disagree.
From the song P.I.M.P:
Snoop Dogg: "Why should we allow you in the PIMP legion of doom?"
50 Cent: "Man whoever said progress was a slow process wasn't talking about me! I'm a P.I.M.P! Plus... I got the magic stick."
*All of a sudden the location changes*
Voice in chorus: "G-G-G-G-G- UNIT!!"