Green’s Dictionary of Slang

1. an act of inhalation of cocaine or from a crack pipe.

1994		Source July 56: [heading] A Megablast from the Past: Cocaine’s Greatest Hits.
1995		Public Enemy ‘Megablast’ 🎵, Yo! Bum Rush The Show [album] Ya should have kept yo ass away from that blast / MEGABLAST!

2. an extremely exciting, satisfying experience.

1988

Bomb the Bass [song title] Megablast.