It is, surely, no more than an elaboration of _blow_: to leave. Nor is it especially new. 1967-8 Baker et al _College Undergraduate Slang Study_ 83: Blow this garage - Leave a place 1996 Eble _Slang & Sociability_ 51: These are a few of the many ways that a college student can say ‘leave’: blow, blow this popsicle stand, [etc.] Jonathon Green