From the link you just posted:
"A lot of bullshit jobs are just manufactured middle-management positions with no real utility in the world, but they exist anyway in order to justify the careers of the people performing them. But if they went away tomorrow, it would make no difference at all.
And that’s how you know a job is bullshit: If we suddenly eliminated teachers or garbage collectors or construction workers or law enforcement or whatever, it would really matter. We’d notice the absence. But if bullshit jobs go away, we’re no worse off."
Yes, he claims that also many people know that their job is "bullshit", but clearly that is not a necessary and sufficient condition. Believing your job is bullshit might be a necessary piece of his definition of a bullshit job, but that makes my objection to his definition even stronger.
My problem is, he is focusing on the individual job - not the industries. Graeber seemed to think there are some vast class of jobs that can disappear in any given company, e.g. in middle management, but it is simply not the case that companies are that overstaffed. Even if the person believes their job is "bullshit", it doesn't mean that it isn't bringing value. Trust me, if you really could cut 50% of all middle manager positions and the company would still go along fine, it would happen.