Green’s Dictionary of Slang

1. (Aus./US) to leave, to depart.

1914		Sport (Adelaide) 8 May 4/5: Why didn’t you blow off on Sunday night, Alice C? I am sure you were not wanted .
1946		E. Wilson Pikes Peek or Bust 231: ‘As we are blowin’ the joint off, Toots sees a broken-down old doorman standing there’.
2010		A. Steinberg Running the Books 58: At 3 p.m. [...] much of the civilian staff blew off for the the day.

2. (US campus) to play truant.

1980		Eble Campus Sl. Fall 1: blow off – fail to attend.
1989		J. Doyle College Sl. Dict. 🌐 blow off [Princeton] to cut, to not go.
1994		Eble Campus Sl. Apr. 2: blow off – disregard, neglect, omit: ‘I blew off my homework to watch television’.
1996		Eble Sl. and Sociability 30: Athough English has dozens of particles available for word building, almost all of the examples in college slang use out, on, off and up: [...] blow off ‘miss class, ignore responsibility’.
2015		J. Stahl OG Dad 193: My daughter got her first bill today. Twenty-five dollars, a cancellation fee for blowing off an appointment with a Dr Papoolian.