Like lint from the sleeve of time….
Dear Word Detective: Recently, I found myself scheduled to be in two places at the same time. Since one was in Southern California, and the other in Seattle, I had to choose. After some thought, I said to my wife “I think I’ll blow off the book club meeting.” The sense of the term “blow off” is to cancel, or simply not attend. Is this a new-ish term in the language? I’ve tried to imagine how it could come about, but the only image I have is “blowing the head off a pint,” and I’m not sure that actually happens except in novels. — Jim Brown.
Or cowboy movies, right? Beats me whether anyone really does that. I dimly remember blowing the foam off a glass of root beer in my youth with mixed (and sticky) results, but I failed to show up for the beer-in-bars class in my 20s, and I’m afraid to try it now. People would know and mock me. It’s like that dream everyone has where you realize you’ve forgotten one course all semester until finals week. Of course, I actually did that once in real life, so I’m a little sensitive.
The specific sense of “blow off” that you note, explained by the Oxford English Dictionary (OED) as “to shirk or evade (a job or duty), to stay away from (school or work) without permission or good reason,” is arguably “new-ish.” The earliest unambiguous print citation found so far for that sense comes from 1968 (“I’m a cop, plain and simple. But I’m just cop enough to blow off a job I don’t want to get fixed into.” Mickey Spillane, “Killer Mine”). But Budd Schulberg used “blow off” in a similar sense, that of “to rebuff, to reject the advances of (a person); to ignore, disregard, dismiss” (OED) in his 1947 prizefighting novel “The Harder They Fall” (“I was just thinking like a moon-struck freshman when I was … deciding to blow Nick off.”). I don’t remember hearing “blow off” in the sense you mention before the late 1970s or early 80s, but that proves exactly nothing. Both senses of “blow off” imply an abrupt and somewhat casual rejection, as if blowing a bit of lint from one’s sleeve.
It’s difficult to pinpoint the date of the appearance of that sense because there are other slang and colloquial senses of the phrase “blow off” cluttering the landscape. One of the most popular is “blow off” meaning, literally, to let steam, gas, etc., under great pressure (in a tank, pipeline, boiler, etc.) escape forcefully, producing a loud noise. The figurative use of this sense to mean “to give vent to or forcefully get rid of anger, emotion, excitement, etc.” in forms such as “blow off steam” has been common in popular speech since the early 1800s (“The widow … sat … fuming and blowing off her steam.” 1836).
“Blow off” has also been used in the same sense as the more common “blow over,” meaning to pass away without serious consequences of lasting effect (“Do they think that … this dreadfull Sentence [shall] blow off without Execution?” 1692). The original metaphor here was an allusion to storm clouds that pass overhead without producing rain.
“Blow off” can also be a noun (usually hyphenated “blow-off”) meaning either a literal “blowing off” of steam, etc., or, figuratively, an outburst or argument (“A blow-off in this wise [i.e. swearing at golf] does one good now and then.” 1898). This sense is synonymous with “blow-up,” but one could make a case for the noun “blow-off” being used to mean the act of (or an instance of ) “blowing off” an obligation (e.g., “I’m sick of Ted, so let’s just give his party the blow-off and go to the movies.”).