To G-rahn is to fall asleep or pass out in any seating while watchingtelevision. This can be intentional or unintentional and the choice will more likely be to stay in the seat than to choose a more preferrable location, such as a bed.
'Grah Grah Boom' is a sound made by only the hardest drill rappers and crazies on the streets.
It is an onomatopoeia for loud, hard hitting gunshots, particularly from a large caliber firearm that can decapitate the average gangbanger with a single bullet. It is frequently used as an adlib in various rap videos.
It can also be used to threaten someone, especially other rival gang members (Mostly in the Bronx or Chicago) with a gun, or to diss dead gang members.